Objective for microscope

ABSTRACT

An objective includes, in order from an object side, first, second, and third lens groups. The first lens group includes, in order from the object side, a first lens, a second lens, and a third lens component. When NA represents an objective numerical aperture, f represents an objective focal length, f G1  represents a first lens group focal length, r 11  represents a radius of curvature of a lens surface on the object side of the first lens, r 12  represents a radius of curvature of a lens surface on an image side of the first lens, and d 012  represents a distance on an optical axis from a front-side focal plane of the objective to a lens surface on the image side of the first lens, the objective satisfies: 
       0.8≦ NA &lt;1,
 
       1.6≦ f   G1   /f ≦6,
 
       −1.6≦ r   11   /f ≦−0.2, and
 
       −2≦ r   12   /d   012 ≦−0.86.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation application of U.S. Ser. No.14/885,223, filed Oct. 16, 2015, which is based upon and claims thebenefit of priority from prior Japanese Patent Application No.2014-217747, filed Oct. 24, 2014, the entire contents of both of whichare incorporated herein by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an objective for a microscope.

Description of the Related Art

In recent years, the number of pixels of an image sensor has increasedremarkably, and in the field of a microscope, expectations for amicroscope device that enables observation and image acquisition whileachieving both a wide field of view and high resolving power areincreasing. As an example, when such a microscope device is employed fora virtual slide, a scanning speed can be increased.

In order to realize the microscope device above, an objective having awide field of view (namely, a large field number and a lowmagnification) and a high numerical aperture is desired. Such anobjective is described, for example, in Japanese Laid-Open PatentPublication No. 2010-186162 and Japanese Laid-Open Patent PublicationNo. 2011-75982.

SUMMARY OF THE INVENTION

An aspect of the present invention is a dry objective for a microscope.The objective includes, in order from an object side, a first lens groupwith positive refractive power, a second lens group with positiverefractive power, the second lens group including a cemented lens thatis configured of a lens with positive refractive power that is made of alow dispersion material and a lens with negative refractive power thatis made of a high dispersion material, and a third lens group withnegative refractive power. The first lens group includes, in order fromthe object side, a first lens that is a single lens having a meniscusshape with a concave surface facing the object side, a second lens thatis a single lens with positive refractive power, the single lens havinga meniscus shape with a concave surface facing the object side, and athird lens component that is a single lens or cemented lens withpositive refractive power. When NA represents a numerical aperture ofthe objective, f represents a focal length of the objective, f_(G1)represents a focal length of the first lens group, r₁₁ represents aradius of curvature of a lens surface on the object side of the firstlens, r₁₂ represents a radius of curvature of a lens surface on an imageside of the first lens, and d₀₁₂ represents a distance on an opticalaxis from a front-side focal plane of the objective to the lens surfaceon the image side of the first lens, the objective satisfies thefollowing conditional expressions:

0.8≦NA<1   (4)

1.6≦f _(G1) /f≦6   (5)

−1.6≦r ₁₁ /f≦−0.2   (6)

−2≦r ₁₂ /d ₀₁₂≦−0.86.   (7)

Another aspect of the present invention is an immersion type objectivefor a microscope. The objective includes, in order from an object side,a first lens group with positive refractive power, a second lens groupwith positive refractive power, the second lens group including acemented lens that is configured of a lens with positive refractivepower that is made of a low dispersion material and a lens with negativerefractive power that is made of a high dispersion material, and a thirdlens group with negative refractive power. The first lens groupincludes, in order from the object side, a first lens that is a singlelens having a meniscus shape with a concave surface facing the objectside, or a first cemented lens that is configured of the first lens anda lens arranged on the object side of the first lens, a second lens thata single lens with positive refractive power, the single lens having ameniscus shape with a concave surface facing the object side, and athird lens component that is a single lens or cemented lens withpositive refractive power. The third lens group includes a rear lensgroup with negative refractive power closest to an image side, and therear lens group includes a fourth lens component that is a single lensor cemented lens having a meniscus shape with a concave surface facingthe object side, and a fifth lens component that is arranged closer tothe object side than the fourth lens component and that is a single lensor cemented lens with negative refractive power with a concave surfacefacing the object side. When NA represents a numerical aperture of theobjective, f represents a focal length of the objective, f_(G1)represents a focal length of the first lens group, r12 represents aradius of curvature of a lens surface on the image side of the firstlens, and d₀₁₂ represents a distance on an optical axis from afront-side focal plane of the objective to the lens surface on the imageside of the first lens, the objective satisfies the followingconditional expressions:

0.8≦NA≦1.5   (8)

2.3≦f _(G1) /f≦8   (9)

−1.5≦r ₁₂ /d ₀₁₂≦−0.75.   (10)

Yet another aspect of the present invention is an objective for amicroscope. The objective includes, in order from an object side, afirst lens group with positive refractive power, a second lens groupwith positive refractive power, and a third lens group with negativerefractive power. When NA represents a numerical aperture of theobjective, FN represents a field number of the objective, β represents amagnification of the objective, ε represents an Airy disk diameter on anaxis to a d-line of the objective, φ_(max) represents a maximum value ofan effective diameter of a lens included in the objective, and h_(exp)represents a radius of an exit pupil of the objective, the objectivesatisfies the following conditional expressions:

0.8≦NA≦1.5   (1)

1000≦FN/|β|/ε≦10000   (2)

1.7≦Φ_(max)/2/h _(exp) /NA≦4.   (3)

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be more apparent from the following detaileddescription when the accompanying drawings are referenced.

FIG. 1 illustrates a configuration of a microscope device according toan embodiment of the present invention.

FIG. 2 is a sectional view of an objective in Example 1 of the presentinvention.

FIG. 3 is a sectional view of a tube lens used in combination with anobjective.

FIG. 4A to FIG. 4D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 2 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 5 is a sectional view of an objective in Example 2 of the presentinvention.

FIG. 6A to FIG. 6D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 5 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 7 is a sectional view of an objective in Example 3 of the presentinvention.

FIG. 8A to FIG. 8D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 7 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 9 is a sectional view of an objective in Example 4 of the presentinvention.

FIG. 10A and FIG. 10D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 9 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 11 is a sectional view of an objective in Example 5 of the presentinvention.

FIG. 12A to FIG. 12D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 11 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 13 is a sectional view of an objective in Example 6 of the presentinvention.

FIG. 14A to FIG. 14D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 13 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 15 is a sectional view of an objective in Example 7 of the presentinvention.

FIG. 16A to FIG. 16D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 15 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 17 is a sectional view of an objective in Example 8 of the presentinvention.

FIG. 18A to FIG. 18D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 17 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 19 is a sectional view of an objective in Example 9 of the presentinvention.

FIG. 20A to FIG. 20D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 19 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 21 is a sectional view of an objective in Example 10 of the presentinvention.

FIG. 22A to FIG. 22D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 21 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

FIG. 23 is a sectional view of an objective in Example 11 of the presentinvention.

FIG. 24A to FIG. 24D are aberration diagrams in a case in which acombination of an objective illustrated in FIG. 23 and a tube lensillustrated in FIG. 3 is used, and respectively illustrate sphericalaberration, a sine condition violation amount, astigmatism, and comaticaberration.

DESCRIPTION OF THE EMBODIMENTS

Objectives described in Japanese Laid-Open Patent Publication No.2010-186162 and Japanese Laid-Open Patent Publication No. 2011-75982insufficiently correct comatic aberration. Therefore, when both a widerfield of view and a high numerical aperture are achieved, or whenvignetting is reduced and an off-axis numerical aperture is enlarged,circumference performance remarkably deteriorates due to comaticaberration. Accordingly, it is difficult to achieve both a wide field ofview and high resolving power at a higher level.

In view of the foregoing, embodiments of the present invention aredescribed below.

FIG. 1 is a schematic diagram illustrating a configuration of amicroscope device 100 according to an embodiment of the presentinvention. The microscope device 100 illustrated in FIG. 1 includes amicroscope body 2, a light source device 3 connected to the microscopebody 2 via an optical fiber 4, an imaging optical system including anobjective 8 and a tube lens 1, and a digital camera incorporating animage sensor 9. The microscope device 100 further includes an XY handle6 that moves a stage 5 in a direction orthogonal to an optical axis ofthe objective 8, and a Z handle 7 that moves the stage 5 in a directionparallel to the optical axis of the objective 8. In addition, themicroscope device 100 may include an eyepiece (not illustrated).

The objective 8 is an infinity correction type objective (a microscopeobjective) for a microscope. The objective 8 may be a dry objective oran immersion type objective. The objective 8 is configured to realize awide field of view (namely, a low magnification and a large fieldnumber) and a high numerical aperture. Specifically, the objective 8 isconfigured so as to satisfy the following conditional expressions,although the other details are described later.

0.8≦NA1.5   (1)

1000≦FN/|β|/ε≦10000   (2)

1.7≦φ_(max)/2/h _(exp) /NA≦4   (3)

In these conditional expressions, NA represents a numerical aperture onan object side of the objective 8. FN represents a field number of theobjective 8. β represents a magnification of the objective 8. εrepresents an Airy disk diameter on an axis to the d-line (588 nm) ofthe objective 8. φ_(max) represents a maximum value of an effectivediameter of a lens included in the objective 8. h_(exp) represents theradius of an exit pupil of the objective 8. The magnification of anobjective corresponds to a projection magnification of a microscopeoptical system formed by combining a tube lens having a focal lengthbetween 160 mm and 200 mm and the objective, which is usually used for amicroscope device. The field number of an objective corresponds to twicethe maximum image height of the microscope optical system above formedby combining the tube lens and the objective. It can be said that, whendigital observation is performed on a sample image formed by thismicroscope optical system by using an image sensor, the objective candeal with an image sensor having a diagonal length that is the same as afield number at the maximum.

Conditional expression (1) represents a condition for obtainingsufficient resolving power. By NA not being less than a lower limitvalue of conditional expression (1), an Airy disk diameter can besufficiently reduced, and therefore sufficient resolving power can beobtained. By NA not being greater than an upper limit value ofconditional expression (1), a spread angle of a marginal ray incident onthe objective 8 does not excessively increase, and deterioration inperformance primarily due to comatic aberration can be suppressed.Accordingly, sufficient resolving power can be obtained.

Conditional expression (2) represents a condition for obtainingsufficient resolving power and a wide field of view. By FN/|β|/ε notbeing less than a lower limit value of conditional expression (2),sample observation and image acquisition can be performed with a widefield of view and high resolving power while making the best use ofperformance of the image sensor 9 having high definition and a largesize (namely, a large number of pixels) that is described later. ByFN/|β|/ε not being greater than an upper limit value of conditionalexpression (2), an Airy disk diameter does not become small enough toexceed resolving power of the image sensor 9, and there is no need tocorrect aberration due to an excessively high NA. Therefore,deterioration in performance primarily due to comatic aberration can besuppressed. A value obtained by dividing a field number of an objectiveby a magnification of the objective is equal to twice the object heightof the objective. Accordingly, when the object height of the objectiveis Y_(ob), conditional expression (2) is synonymous with the followingexpression.

1000≦2×Y _(ob)/ε≦10000   (2A)

Conditional expression (3) represents a condition for satisfactorilycorrecting primarily comatic aberration so as to attain a wide field ofview and high resolving power. By φ_(max)/2/h_(exp)/NA not being lessthan a lower limit value of conditional expression (3), there is no needto converge an off-axis pencil of light with high refractive power in anoptical system in a portion located on a side of a sample S within theobjective 8. Therefore, an incident angle and a refraction angle of anoff-axis marginal ray to a lens surface does not excessively increase,and this allows the generation of comatic aberration to be reduced. Byφ_(max /)2/h_(exp)/NA not being greater than an upper limit value ofconditional expression (3), an outer diameter of a lens configuring theobjective 8 does not excessively increase, and this prevents theobjective 8 from having a large diameter. The pencil of light is abundle of rays emitted from one point of an object (an object point).

It is preferable that the objective 8 satisfy conditional expression(2-1) and conditional expression (3-1) described below, instead ofconditional expression (2) and conditional expression (3) describedabove, respectively, and it is further preferable that the objective 8satisfy conditional expression (2-2) and conditional expression (3-2).

1200≦FN/|β|/ε≦8000   (2-1)

1400≦FN/|β|/ε≦6000   (2-2)

1.9≦φ_(max)/2/h _(exp) /NA≦3.5   (3-1)

2.1≦φ_(max)/2/h _(exp) /NA≦3   (3-2)

The tube lens 1 is a tube lens for a microscope that forms a magnifiedimage of an object (sample S) by being used in combination with theobjective 8. The tube lens 1 is configured so as to satisfactorilycorrect aberration and realize a large field number and a high numericalaperture.

The image sensor 9 is, for example, a CCD (Charge Coupled Device), aCMOS (Complementary Metal Oxide Semiconductor), or the like, and isarranged on an image plane on which a magnified image is formed by theobjective 8 and the tube lens 1.

It is preferable that the image sensor 9 have a large size in order tosufficiently utilize a large field number realized by the objective 8and the tube lens 1. It is also preferable that the image sensor 9 havehigh definition in order to sufficiently exhibit high imagingperformance realized by the objective 8 and the tube lens 1. It ispreferable that the image sensor 9 have, for example, a pixel size L(namely, a length of one side of each pixel) between 1 μm and 17 μm.This is because, when the pixel size L is greater than 17 μm, a Nyquistfrequency is lower than a cut-off frequency of an imaging optical systemand this prevents resolution performance of the imaging optical systemfrom being sufficiently exhibited. This is also because, when the pixelsize L is less than 1 μm, a Nyquist frequency greatly exceeds a cut-offfrequency of the imaging optical system and excessively increases, andresolution performance of an image sensor is not sufficiently exhibited.

In the microscope device 100, the sample S arranged on the stage 5 isilluminated with light that is emitted from the light source device 3and is made incident via the optical fiber 4. The illuminated sample Sis magnified and projected to the image sensor 9 by the objective 8 andthe tube lens 1, and a magnified image of the sample S that has beenformed by the objective 8 and the tube lens 1 is captured by the imagesensor 9. When the microscope device 100 includes an eyepiece, themagnified image of the sample S is observed via the eyepiece.

The microscope device 100 having the above configuration enablesobservation and image acquisition while achieving both a wide field ofview and a high resolution.

A configuration and an action of the objective 8 are described next indetail. The objective 8 is an objective for a microscope that forms amagnified image of an object (the sample S) by being used in combinationwith the tube lens 1. The objective 8 is configured of the first lensgroup with positive refractive power, the second lens group withpositive refractive power, and the third lens group with negativerefractive power in order from the object side.

The first lens group gradually suppresses divergence (spreading) of apencil of light from the object with the positive power. The second lensgroup gradually suppresses spreading of a pencil of divergence lightfrom the first lens group with the positive power while correctingprimarily on-axis chromatic aberration, and converts the pencil ofdivergence light into a pencil of convergence light. The third lensgroup converts the pencil of convergence light from the second lensgroup into a pencil of parallel light with the negative power.

In the objective 8, a ray height of an on-axis marginal ray becomes themaximum within the second lens group. More specifically, the ray heightof the on-axis marginal ray becomes the maximum on a boundary surface ofa lens component closest to the object in the second lens group orwithin the lens component. This characteristic enables a boundarybetween the first lens group and the second lens group, both havingpositive power, to be identified. Further, with regard to a boundarybetween the second lens group and the third lens group, a lens componentwith positive refractive power that is closest to the object among lenscomponents of the objective 8 other than lens components included in thefirst lens group and a lens component which the maximum ray height of anon-axis marginal ray pass through is a lens component closest to theimage plane in the second lens group. This characteristic enables aboundary between the second lens group with positive power and the thirdlens group with negative power to be identified.

In this specification, a lens component is one lens block in which onlytwo surfaces, an object-side surface and an image-side surface, arebrought into contact with air (or immersion liquid), regardless ofwhether this is a single lens or a cemented lens.

When the objective 8 is a dry objective for a microscope, the first lensgroup includes the first lens, the second lens, and the third lenscomponent, in order from the object side. The first lens is a singlelens having a meniscus shape with a concave surface facing the objectside. The second lens is a single lens with positive refractive powerthat has a meniscus shape with a concave surface facing the object side.The third lens component is a single lens or cemented lens with positiverefractive power. The first lens and the second lens may be cemented.

By arranging a single lens having a meniscus shape with a concavesurface facing the object side (the first lens) closest to the object,the concave surface can be arranged in an area in which a marginal rayheight is small. Accordingly, primarily field curvature can besatisfactorily corrected with divergence of a pencil of light from anobject suppressed. Further, by arranging the second lens and the thirdlens each having positive refractive power closer to an image plane thanthe first lens, divergence (spreading) of a pencil of light can begradually suppressed with the generation of spherical aberration andcomatic aberration reduced.

When the objective 8 is an immersion type objective for a microscope,the first lens group includes the first lens or the first cemented lens,the second lens, and the third lens component, in order from the objectside. The first cemented lens is a cemented lens that is configured ofthe first lens and a lens arranged on the object side of the first lens.The first cemented lens and the second lens may be cemented.

By arranging a single lens having a meniscus shape with a concavesurface facing the object side (the first lens) closest to the object,the concave surface can be arranged in an area in which a marginal rayheight is small. Therefore, primarily field curvature can besatisfactorily corrected with divergence of a pencil of light from anobject suppressed. This point is similar to a case of a dry objective.However, in a case of an immersion type objective, it may be difficultto fill a space (a concave portion) formed by the concave surface of thefirst lens with immersion liquid. In this case, a lens that is made of amaterial having a refractive index similar to that of the immersionliquid may be cemented to the concave surface of the first lens.Further, by arranging the second lens and the third lens component eachhaving positive refractive power closer to the image plane than thefirst lens, divergence (spreading) of a pencil of light can be graduallysuppressed with the generation of spherical aberration and comaticaberration reduced. This point is similar to a case of a dry objective.

The second lens group includes a cemented lens that is formed of a lenswith positive refractive power that is made of a low dispersion materialand a lens with negative refractive power that is made of a highdispersion material. The low dispersion material is a material thatsatisfies Abbe number υd≧65. The high dispersion material is a materialthat satisfies Abbe number υd≦55.

In the second lens group, a ray height of a marginal ray is great.Therefore, by the second lens group including a cemented lens that isformed of a lens with positive refractive power that is made of a lowdispersion material and a lens with negative refractive power that ismade of a high dispersion material, on-axis chromatic aberration can beeffectively corrected.

When the objective 8 is an immersion type objective for a microscope,the third lens group includes a rear lens group with negative refractivepower closest to the image plane. The rear lens group includes thefourth lens component, and the fifth component arranged closer to theobject than the fourth lens component. The fourth lens component is asingle lens or cemented lens having a meniscus shape with a concavesurface facing the object side. The fifth lens component is a singlelens or cemented lens with negative refractive power with a concavesurface facing the object side.

The rear lens group in the third lens group converts a pencil of lightinto a pencil of parallel light by using the negative refractive power,and guides the pencil of parallel light to the tube lens 1. By includingthe fourth lens component, the rear lens group can have a concavesurface of a lens arranged in an area in which a marginal ray height issmall. Therefore, the Petzval sum can be corrected in a positivedirection, and field curvature can be satisfactorily corrected. Inaddition, by including the fourth lens component, the rear lens groupcan have an area in which a marginal ray height is small closer to theobject side than the forth lens component. By arranging the fifth lenscomponent with negative refractive power in the area, the Petzval sumcan be corrected in a positive direction, and field curvature can besatisfactorily corrected. Further, because the concave surface faces theobject side, field curvature can be effectively corrected with thegeneration of astigmatism and comatic aberration suppressed.

A preferred configuration of the objective 8 is described below.

It is preferable that the third lens component included in the firstlens group have a meniscus shape with a concave surface facing theobjest side. This enables divergence of a pencil of light to besuppressed while the generation of spherical aberration and comaticaberration is reduced.

Further, it is preferable that the first lens group include the seventhlens component closer to the image plane than the third lens component.The seventh lens component is a single lens or cemented lens withpositive refractive power. By arranging the seventh lens component withpositive refractive power closer to the image plane than the third lenscomponent, an optical system from the first lens to the third lenscomponent can refract a pencil of light more gradually (in a directionin which spreading of the pencil of light is suppressed) in a state inwhich the first lens group has a prescribed refractive power. As aresult, the generation of comatic aberration and spherical aberrationcan be reduced.

It is preferable that the second lens group include three-lens-cementedlenses that is configured by cementing lenses with positive refractivepower that each are made of a low dispersion material on both surfacesof a lens with negative refractive power that is made of a highdispersion material. This configuration enables on-axis chromaticaberration to be corrected on both of the surfaces of the lens withnegative refractive power. Therefore, in the second group in which a rayheight of a merginal ray is great, on-axis chromatic aberration can beeffectively corrected. Further, because a lens surface is cemented toanother lens surface, the generation of spherical aberration and comaticaberration can be reduced.

Further, it is preferable that the second lens group include anaspherical lens that has a lens surface having an aspherical shape. Itis preferable that the aspherical shape be an aspherical shape withpositive refractive power on the optical axis, and be an asphericalshape in which positive refractive power decreases towards a peripheralportion of the lens surface. By arranging the aspherical lens describedabove in the second group in which a ray height of a marginal ray isgreat, spherical aberration and comatic aberration can be satisfactorilycorrected.

It is preferable that the third lens group be configured of a front lensgroup, an intermediate lens group, and a rear lens group, in order fromthe object side. The front lens group is a lens group arranged closestto the object in the third lens group, and has a focal length thatsatisfies conditional expression (12) described later. Thischaracteristic enables a boundary between the front lens group and theintermediate lens group to be identified. The front lens group plays arole in correcting on-axis chromatic aberration while gradually reducinga ray height of a marginal ray that has been converted in a convergencedirection by the second lens group.

The intermediate lens group is a lens group arranged between the frontlens group and the rear lens group. The intermediate lens group plays adifferent role depending on whether the objective 8 is a dry objectiveor an immersion type objective. When the objective 8 is a dry objective,the intermediate lens group plays a role in correcting the Petzval sumin a positive direction and further outputting a pencil of light as apencil of convergence light. This corresponds to actions of animage-side portion of an optical system that is referred to as aso-called gauss group and an object-side portion of an optical systemthat is referred to as a wide converter. When the objective 8 is animmersion type objective, the intermediate lens group plays a role incorrecting the Petzval sum in a positive direction and reducing amarginal ray height of an on-axis pencil of light. This corresponds toan action of an object-side portion of an optical system that isreferred to as a so-called gauss group.

The rear lens group is a lens group arranged closest to the image planein the third lens group. The rear lens group has a differentcharacteristic depending on whether the objective 8 is a dry objectiveor an immersion type objective. When the objective 8 is a dry objective,the rear lens group has negative refractive power, and has acharacteristic whereby an air space between the intermediate lens groupand the rear lens group becomes greatest in the objective 8. When theobjective 8 is an immersion type objective, the rear lens group has acharacteristic whereby an on-axis marginal ray height becomes smallestwithin a lens component closest to the object in the rear lens group oron a boundary surface of the lens component. These characteristicsenable a boundary between the intermediate lens group and the rear lensgroup to be identified. The rear lens group plays a role in convertingan on-axis pencil of light into a pencil of parallel light. Thiscorresponds to actions of an image-side portion of an optical systemthat is referred to as a so-called gauss group and an image-side portionof an optical system that is referred to as a wide converter. The rearlens group also plays a role in correcting the Petzval sum in a positivedirection and converting the on-axis pencil of light into a pencil ofparallel light having a prescribed exit pupil diameter. This correspondsto an action of an image-side portion of an optical system that isreferred to as a so-called gauss group.

It is preferable that the front lens group include the eighth lens andthe ninth lens that are arranged so as to be adjacent to each other. Theeighth lens is a lens with positive refractive power that is made of alow dispersion material, and the ninth lens is a lens with negativerefractive power that is made of a high dispersion material. Aninth-lens-side lens surface of the eighth lens and an eighth-lens-sidelens surface of the ninth lens have a radius of curvature having thesame sign. In other words, lens surfaces adjacent to each other are bentin the same direction.

The front lens group has an action of correcting on-axis chromaticaberration while gradually refracting a marginal ray that has beenconverted in a convergence direction (so as to enter into a convergencestate) by the second lens group so as to reduce a ray height of themarginal ray. By the front lens group having the eighth lens and theninth lens described above, on-axis chromatic aberration can besatisfactorily corrected. By these lenses being arranged so as to beadjacent to each other and by adjacent lens surfaces being bent in thesame direction, the generation of comatic aberration and sphericalaberration can be reduced. The eighth lens and the ninth lens may becemented.

When the objective 8 is a dry objective for a microscope, it ispreferable that the intermediate lens group include the tenth lenscomponent. The tenth lens component is configured of a single lens orcemented lens having a meniscus shape with a concave surface facing theobject side. By arranging the tenth lens component described above in aprescribed position between the front lens group and the rear lensgroup, a ray height of a marginal ray on a concave surface (on theobject side) of the tenth lens component can be smaller than the rayheight of the marginal ray on a convex surface (on the image side). As aresult, the Petzval sum can be corrected in a positive direction, andfield curvature can be satisfactorily corrected. In addition, becausethe concave surface faces the object side, an incident angle and an exitangle of an off-axis pencil of light do not excessively increase, andthe generation of comatic aberration can be reduced.

In this case, it is preferable that the intermediate lens group furtherinclude the thirteenth lens with positive refractive power on the imageside of the tenth lens component. This enables the thirteenth lens tohave a portion of positive refractive power that a convex surface of thetenth lens component originally has, and therefore the generation ofspherical aberration and comatic aberration can be suppressed.

When the objective 8 is an immersion type objective for a microscope, itis preferable that the intermediate lens group include the twelfth lenscomponent. The twelfth lens component is configured of a single lens orcemented lens having a meniscus shape with a convex surface facing theobject side. It is difficult for an immersion type objective for amicroscope to sufficiently correct the Petzval sum on a concave surfaceclosest to the object. Therefore, the third lens group is desired tohave an action of correcting a greater Petzval sum, compared with a casein which the objective 8 is a dry objective for a microscope. Byarranging the twelfth lens component in the intermediate lens group, aray height of a marginal ray on a concave surface (on the image side) ofthe twelfth lens component can be smaller than the ray height of themarginal ray on a convex surface (on the object side). As a result,field curvature can be made satisfactory. Further, because the convexsurface of the twelfth lens component faces the object side, a marginalray height can be reduced in an area on the image side of theintermediate lens group, namely, in an area on the object side of therear lens group. As a result, the Petzval sum can be corrected moreeffectively.

When the objective 8 is a dry objective for a microscope, it ispreferable that the rear lens group have negative refractive power andthat field curvature be satisfactorily corrected by using the negativerefractive power. However, when a radius of curvature of a concavesurface excessively decreases, at least one of comatic aberration andastigmatism is greatly generated. In view of this, it is preferable thatthe rear lens group include two or more lens components with negativerefractive power. By the two or more lens components sharing negativerefractive power, the rear lens group can have a prescribed negativerefractive power, and a radius of curvature of each of the lenscomponents can be prevented from excessively decreasing. As a result,the generation of comatic aberration and astigmatism can be reduced.

When the objective 8 is an immersion type objective, it is preferablethat the rear lens group include the eleventh lens component that isarranged closer to the object than the fourth lens component. Theeleventh lens component is a single lens or cemented lens with negativerefractive power. By the rear lens group including the eleventh lenscomponent with negative refractive power separately from the fourth lenscomponent having an action of correcting the Petzval sum, the generationof astigmatism and comatic aberration can be suppressed, and fieldcurvature can be corrected more effectively.

Regardless of whether the objective 8 is a dry objective for amicroscope or an immersion type objective for a microscope, it ispreferable that the rear lens group include an aspherical lens that hasa lens surface having an aspherical shape. It is preferable that theaspherical shape be an aspherical shape with negative refractive poweron the optical axis, and be an aspherical shape in which negativerefractive power decreases towards a peripheral portion of the lenssurface. By arranging the aspherical lens described above in the rearlens group in which an off-axis ray height is great, field curvature andastigmatism can be effectively corrected. It is also preferable that therear lens group have a diffractive optical element with negativerefractive power. This enables chromatic aberration of magnification tobe satisfactorily corrected. Even when a lens with positive refractivepower that is made of a high dispersion material is arranged in the rearlens group, a similar effect can be attained to some extent. However, byarranging a diffractive optical element, chromatic aberration ofmagnification of a g-line can be more surely prevented from beingexcessively corrected.

Regardless of whether the objective 8 is a dry objective for amicroscope or an immersion type objective for a microscope, it ispreferable that the objective 8 include the sixth lens with positiverefractive power that is made of a material having a high partialdispersion. By the objective 8 including the sixth lens, on-axischromatic aberration of a g-line that is excessively corrected whencorrecting on-axis chromatic aberration by using a combination of alow-dispersion negative lens and a high-dispersion positive lens can besatisfactorily corrected. The material having a high partial dispersionis a material that satisfies (n_(g)−n_(F))/(n_(F)−n_(C))≧0.58, wheren_(g), n_(F), and n_(C) respectively represent refractive indices of amaterial to a g-line, an F-line, and a C-line. As an example, a materialsuch as NBH53, TIH3, or TIH53 of OHARA INC. falls under this material.When the objective 8 is a dry objective for a microscope, it ispreferable that the sixth lens be included in the intermediate lensgroup. In particular, it is preferable that the sixth lens be includedin a meniscus lens component included in the intermediate lens group orthat the sixth lens be arranged on the image side of the meniscus lenscomponent included in the intermediate lens group. In this case, thesixth lens is arranged in an area in which a marginal ray height isrelatively great, and therefore compensation for chromatic aberration ofa g-line that has been excessively corrected as described above andcorrection of field curvature can be performed simultaneously.

Conditions satisfied by the objective 8 are described below.

When the objective 8 is a dry objective, the objective 8 is configuredso as to satisfy conditional expression (4) to conditional expression(7) described below.

0.8≦NA<1   (4)

1.6≦f _(G1) /f≦6   (5)

−1.6≦r ₁₁ /f≦−0.2   (6)

−2≦r ₁₂ /d ₀₁₂≦−0.86   (7)

When the objective 8 is an immersion type objective, the objective 8 isconfigured so as to satisfy conditional expression (8) to conditionalexpression (10) described below.

0.8≦NA≦1.5   (8)

2.3≦f _(G1) /f≦8   (9)

−1.5≦r ₁₂ /d ₀₁₂≦−0.75   (10)

In these conditional expressions, NA represents a numerical aperture ofthe objective 8. f represents a focal length of the objective 8. f_(G1)represents a focal length of the first lens group. r₁₁ represents aradius of curvature of a lens surface on the object side of the firstlens. r₁₂ represents a radius of curvature of a lens surface on theimage side of the first lens. d₀₁₂ represents a distance on the opticalaxis from a front-side focal plane (namely, an object surface) of theobjective 8 to a lens surface on the image side of the first lens.

Conditional expression (4) and conditional expression (8) areconditional expressions required to obtain sufficient resolving power.By NA being not less than lower limit values of conditional expression(4) and conditional expression (8), an Airy disk diameter can be reducedsufficiently, and therefore sufficient resolving power can be obtained.When the objective 8 is a dry objective, NA does not exceed 1. When theobjective 8 is an immersion type objective, a spread angle of a marginalray incident on the objective 8 does not increase excessively by NA notbeing greater than an upper limit value of conditional expression (8),and therefore performance deterioration primarily due to comaticaberration can be suppressed. Accordingly, sufficient resolving powercan be obtained.

Conditional expression (5) and conditional expression (9) areconditional expressions to satisfactorily correct primarily comaticaberration. By f_(m)/f not being less than a lower limit value of aconditional expression according to the type of an objective (a dryobjective or an immersion type objective) (here, conditional expression(5) or conditional expression (9)), a focal length of the first lensgroup does not decrease excessively. This can also prevent a focallength of each of the lenses that configures the first lens group fromdecreasing excessively. As a result, the generation of comaticaberration in the first lens group can be reduced, and comaticaberration of the entirety of the objective 8 can be satisfactorilycorrected. By f_(G1)/f not being greater than an upper limit value ofthe conditional expression, a focal length of the first lens group doesnot increase excessively, and therefore an excessive increase in anoff-axis marginal ray height in the second lens group can be avoided.Accordingly, the generation of comatic aberration in the second lensgroup can be reduced, and comatic aberration of the entirety of anobjective can be satisfactorily corrected. When conditional expression(5) and conditional expression (9) are compared, upper limit values andlower limit values are different from each other. This results from asmaller convergence (spreading suppression) action of a pencil of lightin the first lens group of an immersion type objective, compared with adry objective, because, in the immersion type objective, a lens surfaceclosest to the object is in contact with immersion liquid.

Conditional expression (6) is a conditional expression to satisfactorilycorrect primarily field curvature, spherical aberration, and comaticaberration. By r₁₁/f not being less than a lower limit value ofconditional expression (6), a radius of curvature of a concave surfacethat is a lens surface on the objective side of the first lens does notexcessively increase. Therefore, a correction amount of the Petzval sumin a positive direction does not excessively decrease, and fieldcurvature can be satisfactorily corrected. In addition, incident anglesand refraction angles of on-axis and off-axis marginal rays to a lenssurface do not excessively increase, and therefore spherical aberrationand comatic aberration can be satisfactorily corrected. By r₁₁/f notbeing greater than an upper limit value of conditional expression (6), aradius of curvature of a concave surface that is a lens surface on theobject side of the first lens does not excessively decrease. Therefore,spreading of on-axis and off-axis pencils of light can be suppressedsufficiently, and the generation of spherical aberration and comaticaberration can be reduced on a lens surface on the image side of thefirst lens and in an optical system closer to the image plane than thefirst lens.

Conditional expression (7) and conditional expression (10) areconditional expressions to satisfactorily correct primarily sphericalaberration and comatic aberration. By r₁₂/d_(o12) not being less than alower limit value of a conditional expression according to the type ofan objective (a dry objective or an immersion type objective) (here,conditional expression (7) or conditional expression (10)), a radius ofcurvature of a convex surface that is a lens surface on the image sideof the first lens does not increase excessively. Therefore, spreading ofon-axis and off-axis pencils of light can be suppressed sufficiently,and the generation of spherical aberration and comatic aberration can bereduced in an optical system closer to the image plane than the firstlens. By r₁₂/d₀₁₂ not being greater than an upper limit value of theconditional expression, a radius of curvature of a convex surface thatis a lens surface on the image side of the first lens does not decreaseexcessively. Therefore, incident angles and refraction angles of on-axisand off-axis marginal rays to a lens surface do not increaseexcessively, and as a result, spherical aberration and comaticaberration can be satisfactorily corrected. When conditional expression(7) and conditional expression (10) are compared, upper limit values andlower limit values are different from each other. This results from asmaller convergence (spreading suppression) action of a pencil of lighton an object-side surface of the first lens in an immersion typeobjective than that of a dry objective, because a lens surface closestto the object side in the immersion type objective is in contact withimmersion liquid.

When the objective 8 is a dry objective, it is preferable that theobjective 8 satisfy conditional expression (5-1) to conditionalexpression (7-1) described below, instead of conditional expression (5)to conditional expression (7) described above, respectively, and it isfurther preferable that the objective 8 satisfy conditional expression(5-2) to conditional expression (7-2). When the objective 8 is animmersion type objective, it is preferable that the objective 8 satisfyconditional expression (9-1) and conditional expression (10-1) describedbelow, instead of conditional expression (9) and conditional expression(10) described above, respectively, and it is further preferable thatthe objective satisfy conditional expression (9-2) and conditionalexpression (10-2).

1.9≦f _(G1)/f≦4.5   (5-1)

2.1≦f _(G1) /f≦3.5   (5-2)

−1.53≦r ₁₁ /f≦−0.6   (6-1)

−1.46≦r ₁₁ /f≦−1   (6-2)

−1.75≦r ₁₂ /d ₀₁₂≦−0.95   (7-1)

−1.5≦r ₁₂ /d ₀₁₂≦−1.05   (7-2)

2.55≦f _(G1) /f≦6   (9-1)

2.8≦f _(G1) /f≦4   (9-2)

−1.3≦r ₁₂ /d ₀₁₂≦−0.8   (10-1)

−1.1≦r ₁₂ /d _(012≦−)0.9   (10-2)

Conditions that the objective 8 preferably satisfies are describedbelow.

It is preferable that the objective 8 satisfy conditional expression(11) to conditional expression (14) described below.

0.2≦D _(ogF) D _(0L)≦0.87   (11)

−0.3≦f/f _(G30)≦0.3   (12)

0.05≦f _(G1) /f _(L2)≦0.6   (13)

0.03≦f _(G1) /f _(L3)≦0.5   (14)

In these conditional expressions, D_(ogF) represents a distance on theoptical axis from a front-side focal plane (an object surface) of theobjective 8 to a lens surface on the image side of the sixth lens.D_(oL) represents a distance on the optical axis from a front focalplane (an object surface) of the objective 8 to a lens surface closestto the image plane of the objective 8. f_(G30) represents a focal lengthof a front lens group. f_(L2) represents a focal length of the secondlens. f_(L3) represents a focal length of the third lens component.

Conditional expression (11) is a conditional expression relating to aposition of the sixth lens in the objective 8. By D_(ogF)/D_(oL)satisfying conditional expression (11), the sixth lens can be arrangedin an area in which a marginal ray height is great. Therefore, excessivecorrection of on-axis chromatic aberration of a g-line can beefficiently compensated for. In particular, by D_(ogF)/D_(oL) not beinggreater than an upper limit value of conditional expression (11), thesixth lens can be arranged in an area in which an off-axis principal rayheight is small. Therefore, chromatic aberration of magnification of ag-line can be prevented from being excessively corrected.

Conditional expression (12) is a conditional expression relating to afocal length of a rear lens group. By f/f_(G30) not being greater thanan upper limit value of conditional expression (12), a convergenceaction of the rear lens group does not excessively increase. Therefore,a marginal ray can gradually pass through the rear lens group withoutbeing suddenly refracted. As a result, on-axis chromatic aberration canbe effectively corrected while the generation of comatic aberration andspherical aberration is reduced. By f/f_(G30) not being less than alower limit value of condition expression (12), a divergence action inthe rear lens group does not excessively increase, and a marginal rayheight can be sufficiently reduced within the rear lens group and in anoptical system closer to the image plane than the rear lens group.

Conditional expression (13) is a conditional expression tosatisfactorily correct primarily comatic aberration and sphericalaberration. By f_(G1)/f_(L2) not being greater than an upper limit valueof conditional expression (13), a focal length of the second lens doesnot excessively decrease. Therefore, divergence (spreading) of a pencilof light can be gradually suppressed while the generation of sphericalaberration and comatic aberration is reduced. By f_(G1)/f_(L2) not beingless than a lower limit value of conditional expression (13), a focallength of the second lens does not excessively increase. Therefore, thefirst lens group can have prescribed refractive power without anexcessive increase in refractive power of other positive lenses thatconfigure the first lens group. Therefore, in the first lens group,divergence (spreading) of a pencil of light can be gradually suppressedwhile the generation of spherical aberration and comatic aberration isreduced.

Conditional expression (14) is a conditional expression tosatisfactorily correct primarily comatic aberration and sphericalaberration. By f_(G1)/f_(L3) not being greater than an upper limit valueof conditional expression (14), a focal length of the third lenscomponent does not excessively decrease. Therefore, divergence(spreading) of a pencil of light can be gradually reduced while thegeneration of spherical aberration and comatic aberration is reduced. Byf_(G1)/f_(L3) not being less than a lower limit value of conditionalexpression (14), a focal length of the third lens component does notexcessively increase. The first lens group can have prescribedrefractive power without an excessive increase in refractive power ofother positive lenses that configure the first lens group. Therefore, inthe first lens group, divergence (spreading) of a pencil of light can begradually suppressed while the generation of spherical aberration andcomatic aberration is reduced.

It is preferable that the objective 8 satisfy conditional expression(11-1) to conditional expression (14-1) described below, instead ofconditional expression (11) to conditional expression (14) describedabove, respectively, and it is further preferable that the objective 8satisfy conditional expression (11-2) to conditional expression (14-2).

0.3≦D _(ogF) /D _(oL)≦0.83   (11-1)

0.38≦D _(ogF) /D _(oL)≦0.75   (11-2)

−0.25≦f/f _(G30)≦0.2   (12-1)

−0.2≦f/f _(G30)≦0.11   (12-2)

0.1≦f _(G1) /f _(L2)≦0.5   (13-1)

0.15≦f _(G1) /f _(L2)≦0.4   (13-2)

0.05≦f _(G1) /f _(L3)≦0.4   (14-1)

0.07≦f _(G1) /f _(L3)≦0.3   (14-2)

When the objective 8 is a dry objective, it is preferable that theobjective 8 satisfy conditional expression (15) and conditionalexpression (16) described below.

−10≦f _(G3I) /f≦−1.5   (15)

0.8≦r ₂₁ /r ₁₂≦2   (16)

In these conditional expressions, f_(G3I) represents a focal length ofthe rear lens group. r12 represents a radius of curvature of a lenssurface on the image side of the first lens. r₂₁ represents a radius ofcurvature of a lens surface on the object side of the second lens.

Conditional expression (15) is a conditional expression tosatisfactorily correct primarily field curvature.

Considering that light from the rear lend group is parallel light, byf_(G3I)/f not being less than a lower limit value of conditionalexpression (15), a marginal ray height in the rear lens group can besufficiently reduced, compared with a lens group closer to the objectthan the rear lens group. In addition, the rear lens group can havesufficient negative refractive power, and therefore a correction amountof the Petzval sum in a positive direction does not excessivelydecrease, and field curvature can be satisfactorily corrected. Byf_(G3I)/f not being greater than an upper limit value of conditionalexpression (15), negative refractive power of the rear lens group doesnot excessively increase, and a marginal ray height does not excessivelyincrease in a lens group closer to the object than the rear lens group.Therefore, the generation of comatic aberration and spherical aberrationcan be reduced.

Conditional expression (16) is a conditional expression tosatisfactorily correct primarily spherical aberration and comaticaberration. By r₂₁/r₁₂ not being greater than an upper limit value ofconditional expression (16), a radius of curvature of a concave surfacethat is a lens surface on the object side of the second lens does notexcessively increase. Therefore, incident angles and refraction anglesof on-axis and off-axis marginal rays to the lens surface do notexcessively increase, and spherical aberration and comatic aberrationcan be satisfactorily corrected. By r₂₁/r₁₂ not being less than a lowerlimit value of conditional expression (16), a radius of curvature of aconcave surface that is a lens surface on the object side of the secondlens does not excessively decrease. Therefore, divergence (spreading) ofon-axis and off-axis pencils of light can be sufficiently suppressed.

It is preferable that the objective 8 satisfy conditional expression(15-1) and conditional expression (16-1) described below, instead ofconditional expression (15) and conditional expression (16) describedabove, respectively, and it is further preferable that the objective 8satisfy conditional expression (15-2) and conditional expression (16-2).

−7.5≦f _(G3I) /f≦−2   (15-1)

−5≦f _(G3I) /f≦−2.5   (15-2)

1≦r ₂₁ /r ₁₂ ≦1.7   (16-1)

1.2≦r ₂₁ /r ₁₂≦1.4   (16-2)

When the objective 8 is a dry objective, an arbitrary combination ofconditional expression (11) to conditional expression (16) may beadopted for an objective that satisfies conditional expressions (4) to(7). When the objective 8 is an immersion type objective, an arbitrarycombination of conditional expression (11) to conditional expression(14) may be adopted for an objective that satisfies conditionalexpressions (8) to (10). Respective expressions may be limited merely byone of an upper limit value and a lower limit value.

The objective 8 can realize a microscope objective having a wide fieldof view and a high numerical aperture with aberration satisfactorilycorrected. Examples of the objective 8 above are described below indetail. Example 1 to Example 5 describe a dry objective, and Example 6and examples that follow describe an immersion type objective.

EXAMPLE 1

FIG. 2 is a sectional view of an objective 11 in this example. Theobjective 11 illustrated in FIG. 2 is a dry objective for a microscope.The objective 11 is configured of the first lens group G1 with positiverefractive power, the second lens group G2 with positive refractivepower including a cemented lens that is configured of a lens withpositive refractive power that is made of a low dispersion material anda lens with negative refractive power that is made of a high dispersionmaterial, and the third lens group G3 with negative refractive power, inorder from the object side.

The first lens group G1 is configured of a cemented lens CL1 that isconfigured of a meniscus lens L1 (the first lens) with negativerefractive power with a concave surface facing the object side and ameniscus lens L2 (the second lens) with positive refractive power with aconcave surface facing the object side, a cemented lens CL2 (the thirdlens component) that is configured of a meniscus lens L3 with negativerefractive power with a concave surface facing the object side and ameniscus lens L4 with positive refractive power with a concave surfacefacing the object side, and a cemented lens CL3 (the seventh lenscomponent) that is configured of a meniscus lens L5 with negativerefractive power with a concave surface facing the object side and ameniscus lens L6 with positive refractive power with a concave surfacefacing the object side, in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL4that is configured of a biconvex lens L7, a biconcave lens L8, and abiconvex lens L9, and a cemented lens CL5 that is configured of ameniscus lens L10 with negative refractive power with a concave surfacefacing the image side and a biconvex lens L11, in order from the objectside.

The third lens group G3 is configured of the 3o-th lens group (the frontlens group), the 3c-th lens group (the intermediate lens group), and the3i-th lens group (the rear lens group), in order from the object side.The 3o-th lens group is configured of a meniscus lens L12 with negativerefractive power with a concave surface facing the image side, abiconvex lens L13 (the eighth lens), and a meniscus lens L14 (the ninthlens) with negative refractive power with a concave surface facing theobject side, in order from the object side. The 3c-th lens group isconfigured of a cemented lens CL6 (the tenth lens component) that isconfigured of a meniscus lens L15 with negative refractive power with aconcave surface facing the object side and a meniscus lens L16 (thesixth lens; NBH53 of OHARA INC.) with positive refractive power with aconcave surface facing the object side, and a biconvex lens L17, inorder from the object side. The 3i-th lens group is configured of ameniscus lens L18 with negative refractive power with a concave surfacefacing the image side, and a cemented lens CL7 that is configured of ameniscus lens L19 with negative refractive power with a concave surfacefacing the object side and a meniscus lens L20 with positive refractivepower with a concave surface facing the object side, in order from theobject side.

Various pieces of data of the objective 11 are described below. Thed-line (587.56 nm) is used for a reference wavelength. f_(G2) representsa focal length of the second lens group G2, and f_(L7) represents afocal length of the seventh lens component. E represents a power of 10.

NA=0.85, FN=30 mm, |β|=20, ε=8.43E−04 mm, f=9 mm, f_(G1)=30.11 mm,r₁₁=−12.2481 mm, r₁₂=−17.8211 mm, d_(o12)=12.182 mm, Φ_(max)/2=19.05 mm,h_(exp)=7.65 mm, f_(G30)=−196.64 mm, f_(G3I)=−30.23 mm, r₂₁ =−17.8211mm, D_(oL)=133.000 mm, D_(ogF)=90.312 mm, f_(L2)=196.11 mm, f_(L3)=66.55mm

Lens data of the objective 11 is described below. “INF” in the lens datarepresents infinity (∞).

Objective 11 s r d nd νd er s1(object INF 0.150 1.52100 56.02 0.75surface) s2 INF 1.942 0.85 s3 −12.2481 10.090 1.88300 40.76 3.39 s4−17.8211 4.612 1.60300 65.44 9.46 s5 −16.9951 0.100 11.64 s6 −23.70811.043 1.63779 42.41 12.48 s7 −28.2010 5.361 1.60300 65.44 13.32 s8−16.3520 0.100 13.94 s9 −40.7739 0.838 1.63779 42.41 15.49 s10 −55.99454.018 1.49702 81.54 16.04 s11 −28.6925 0.100 16.46 s12 35.2415 14.3081.43876 94.93 18.69 s13 −30.8526 1.500 1.63779 42.41 18.54 s14 72.95608.018 1.43876 94.93 18.97 s15 −42.3220 0.100 19.05 s16 50.1825 1.3001.63779 42.41 18.26 s17 20.2794 11.485 1.43876 94.93 16.84 s18 −94.58550.200 16.77 s19 101.8945 1.000 1.63779 42.41 16.26 s20 33.4896 0.10015.67 s21 30.4321 7.731 1.43876 94.93 15.70 s22 −50.4634 0.624 15.62 s23−42.0010 1.000 1.67305 38.15 15.59 s24 −1706.2591 5.818 15.61 s25−23.7887 1.891 1.48751 70.23 15.61 s26 −162.4849 6.884 1.73806 32.2617.41 s27 −31.7625 4.144 17.95 s28 74.7972 5.430 1.63779 42.41 17.18 s29−199.8224 25.089 16.83 s30 290.9229 1.000 1.49702 81.54 9.57 s31 34.88785.025 9.16 s32 −15.6607 1.000 1.49702 81.54 9.02 s33 −663.5991 1.0001.63779 42.41 9.51 s34 −53.4597 −23.576 9.54

Here, s represents a surface number, r represents a radius of curvature(mm), d represents a surface spacing (mm), nd represents a refractiveindex to the d-line, υd represents an Abbe number, and er represents aneffective radius (mm). These symbols are similar in the followingexamples. Surfaces represented by surface numbers s1 and s2 arerespectively an object surface (a surface on the object side of a coverglass) and a surface on the image side of the cover glass, and surfacesrepresented by surface numbers s3 and s34 are respectively a lenssurface closest to the object and a lens surface closest to the imageplane in an objective. As an example, surface spacing d1 represents adistance from a surface represented by surface number s1 to a surfacerepresented by surface number s2. A last value of a surface spacingrepresents a distance from a lens surface closest to the image plane inan objective to an exit pupil position. A minus value represents that anexit pupil position is located closer to the object than a lens surfaceclosest to the image plane in an objective.

The objective 11 satisfies conditional expressions (1) to (7) and (11)to (16), as described below. A field number FN and a magnification β arevalues in a case in which the objective 11 is used in combination withthe tube lens 10. This point is similar in all of Example 1 to Example11.

NA=0.85   (1), (4):

FN/|β|/ε=1780   (2):

Φ_(max)/2/h_(exp) /NA=−2.93   (3):

f _(c1) /f=3.35   (5):

r ₁₁ /f=−1.36   (6):

r ₁₂ /d ₀₁₂=−1.46   (7):

D _(ogF) /D _(oL)=0.68   (11):

f/f _(G30)=−0.05   (12):

f _(G1) /f _(L2)=0.15   (13):

f _(G1) /f _(L3)=0.45   (14):

f _(G3I) /f=−3.36   (15):

r ₂₁ /r ₁₂=1.00   (16):

FIG. 3 is a sectional view of the tube lens 10 used in combination withthe objective 11. FIG. 4A to FIG. 4D are aberration diagrams in a casein which a combination of the objective 11 and the tube lens 10illustrated in FIG. 3 is used. FIG. 4A illustrates spherical aberration,FIG. 4B illustrates a sine condition violation amount, FIG. 4Cillustrates astigmatism, and FIG. 4D illustrates comatic aberration. Inthese diagrams, “M” represents a meridional component, and “S”represents a sagittal component. Respective aberration diagramsincluding diagrams in Example 2 and examples that follow illustrateaberration that is output when the first surface s1 of the tube lens 10is made to coincide with an exit pupil position of an objective. Aconfiguration of the tube lens 10 illustrated in FIG. 3 is describedlater.

EXAMPLE 2

FIG. 5 is a sectional view of an objective 12 in this example. Theobjective 12 illustrated in FIG. 5 is a dry objective for a microscope.The objective 12 is configured of the first lens group G1 with positiverefractive power, the second lens group G2 with positive refractivepower that includes a cemented lens that is configured of a lens withpositive refractive power that is made of a low dispersion material anda lens with negative refractive power that is made of a high dispersionmaterial, and the third lens group G3 with negative refractive power, inorder from the object side.

The first lens group G1 is configured of a meniscus lens L1 (the firstlens) with negative refractive power with a concave surface facing theobject side, a meniscus lens L2 (the second lens) with positiverefractive power with a concave surface facing the object side, ameniscus lens L3 (the third lens component) with positive refractivepower with a concave surface facing the object side, and a meniscus lensL4 (the seventh lens component) with positive refractive power with aconcave surface facing the object side, in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL1that is configured of a biconvex lens L5, a biconcave lens L6, and abiconvex lens L7, and a cemented lens CL2 that is configured of ameniscus lens L8 with negative refractive power with a concave surfacefacing the image side and a biconvex lens L9, in order from the objectside.

The third lens group G3 is configured of the 3o-th lens group (the frontlens group), the 3c-th lens group (the intermediate lens group), and the3i-th lens group (the rear lens group), in order from the object side.The 3o-th lens group is configured of a cemented lens CL 3 that isconfigured of a meniscus lens L10 (the ninth lens) with negativerefractive power with a concave surface facing the image side and ameniscus lens L11 (the eighth lens) with positive refractive power witha concave surface facing the image side, and a meniscus lens L12 withnegative refractive power with a concave surface facing the image side,in order from the object side. The 3c-th lens group is configured of acemented lens CL4 (the tenth lens component) that is configured of ameniscus lens L13 with negative refractive power with a concave surfacefacing the object side and a meniscus lens L14 (the sixth lens; NBH53 ofOHARA INC.) with positive refractive power with a concave surface facingthe object side, and a biconvex lens L15, in order from the object side.The 3i-th lens group is configured of a biconcave lens L16, and ameniscus lens L17 with negative refractive power with a concave surfacefacing the object side, in order from the object side.

Various pieces of data of the objective 12 are described below. Thed-line (587.56 nm) is used for a reference wavelength.

NA=0.9, FN=30 mm, |β|=20, ε=7.96E−04 mm, f=9 mm, f_(G1)=19.422 mm,r₁₁=−9.8587 mm, r₁₂=−13.0211 mm, d_(o12)=11.431 mm, Φ_(max)/2−16.15 mm,h_(exp)=8.10 mm, f_(G30)−−52.9824 mm, f_(G3I)=−29.147 mm, r₂₁=−16.8701mm, D_(cL)=100.382 mm, D_(ogF)=82.791 mm, f₁₂=57.08 mm, f_(L3)=238.45 mm

Lens data of the objective 12 is described below.

Objective 12 s r d nd νd er s1(object INF 0.150 1.52100 56.02 0.75surface) s2 INF 1.390 0.86 s3 −9.8587 9.891 1.88300 40.76 2.93 s4−13.0211 1.258 8.83 s5 −16.8701 3.652 1.67790 55.34 9.99 s6 −12.77600.100 10.77 s7 −20.8962 3.754 1.60300 65.44 11.78 s8 −19.4778 0.10013.02 s9 −55.3230 2.940 1.49700 81.54 14.08 s10 −28.0702 0.100 14.33 s1124.5700 8.491 1.43875 94.93 16.06 s12 −80.5777 0.800 1.63775 42.41 15.92s13 19.5830 10.948 1.43875 94.93 14.97 s14 −38.5327 0.100 15.01 s1527.6315 0.800 1.63775 42.41 14.10 s16 14.3420 10.337 1.43875 94.93 12.71s17 −46.3046 0.200 12.60 s18 22.3981 0.800 1.63775 42.41 11.38 s1911.2096 5.812 1.49700 81.54 9.98 s20 45.0258 0.100 9.77 s21 44.94550.800 1.63775 42.41 9.74 s22 15.3887 7.272 9.03 s23 −11.7080 0.8001.48749 70.23 9.03 s24 −45.2675 12.197 1.73800 32.26 10.38 s25 −20.23310.100 13.21 s26 82.3763 3.191 1.67790 55.34 13.16 s27 −65.0281 9.35413.10 s28 −80.8182 0.800 1.49700 81.54 10.35 s29 37.0824 3.163 9.98 s30−31.4348 0.983 1.49700 81.54 9.96 s31 −254.1359 −25.918 10.13

The objective 12 satisfies conditional expressions (1) to (7) and (11)to (16), as described below.

NA=0.9   (1), (4):

FN/|β|/ε =1885   (2):

Φ_(max)/2/h_(exp) /NA=2.22   (3):

f _(G1) /f=2.16   (5):

r ₁₁ /f=−1.10   (6):

r ₁₂ /d ₀₁₂=−1.14   (7):

D _(ogF) /D _(oL)=0.82   (11):

f/f _(G30)=−0.17   (12):

f _(G1) /f _(L2)=0.34   (13):

f _(G1) /f _(L3)=0.08   (14):

f _(G3I) /f=−3.24   (15):

r₂₁ /r ₁₂=1.30   (16):

FIG. 6A to FIG. 6D are aberration diagrams in a case in which acombination of the objective 12 and the tube lens 10 is used. FIG. 6Aillustrates spherical aberration, FIG. 6B illustrates a sine conditionviolation amount, FIG. 6C illustrates astigmatism, and FIG. 6Dillustrates comatic aberration.

EXAMPLE 3

FIG. 7 is a sectional view of an objective 13 in this example. Theobjective 13 illustrated in FIG. 7 is a dry objective for a microscope.The objective 13 is configured of the first lens group G1 with positiverefractive power, the second lens group G2 with positive refractivepower that includes a cemented lens that is configured of a lens withpositive refractive power that is made of a low dispersion material anda lens with negative refractive power that is made of a high dispersionmaterial, and the third lens group G3 with negative refractive power, inorder from the object side.

The first lens group G1 is configured of a meniscus lens L1 (the firstlens) with negative refractive power with a concave surface facing theobject side, a meniscus lens L2 (the second lens) with positiverefractive power with a concave surface facing the object side, ameniscus lens L3 (the third lens component) with positive refractivepower with a concave surface facing the object side, and a meniscus lensL4 (the seventh lens component) with positive refractive power with aconcave surface facing the object side, in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL1that is configured of a biconvex lens L5, a biconcave lens L6, and abiconvex lens L7, and a cemented lens CL2 that is configured of ameniscus lens L8 with negative refractive power with a concave surfacefacing the image side and a biconvex lens L9, in order from the objectside.

The third lens group G3 is configured of the 3o-th lens group (the frontlens group), the 3c-th lens group (the intermediate lens group), and the3i-th lens group (the rear lens group), in order from the object side.The 3o-th lens group is configured of a cemented lens CL3 that isconfigured of a meniscus lens L10 (the ninth lens) with negativerefractive power with a concave surface facing the image side and abiconvex lens L11 (the eighth lens), and a biconcave lens L12, in orderfrom the object side. The 3c-th lens group is configured of a cementedlens CL 4 (the tenth lens component) that is configured of a meniscuslens L13 with negative refractive power with a concave surface facingthe object side and a meniscus lens L14 (the sixth lens; NBH53 of OHARAINC.) with positive refractive power with a concave surface facing theobject side, and a biconvex lens L15, in order from the object side. The3i-th lens group is configured of a biconcave lens L16, and a cementedlens CL5 that is configured of a biconcave lens L17 and a biconvex lensL18, in order from the object side.

Various pieces of data of the objective 13 are described below. Thed-line (587.56 nm) is used for a reference wavelength.

NA=0.95, FN=30 mm, |β|=20, ε=7.54E−04 mm, f=9 mm, f_(G1)=27.3 mm,r₁₁=−13.0828 mm, r₁₂=−18.6447 mm, d_(o12)=13.101 mm, Φ_(max)/2=23.948mm, h_(exp)=8.55 mm, f_(G2)=54.7 mm, f_(G30)=159.94 mm, f_(G3C)=65.94mm, f_(G3I)=−31.75 mm, r₂₁=−25.0446 mm, D_(oL)=148.679 mm,D_(ogF)=108.374 mm, f_(L2)=82.66 mm, f_(L3)=109.35 mm, f_(L7)=156.84 mm

Lens data of the objective 13 is described below.

Objective 13 s r d nd νd er s1(object INF 0.150 1.52100 56.02 0.75surface) s2 INF 2.027 0.87 s3 −13.0828 10.924 1.88300 40.76 4.37 s4−18.6447 1.191 11.63 s5 −25.0446 4.866 1.60300 65.44 13.27 s6 −17.88740.110 14.45 s7 −23.8656 5.582 1.60300 65.44 15.60 s8 −19.0650 0.11016.72 s9 −74.2737 3.752 1.49700 81.54 19.54 s10 −38.6719 0.110 19.84 s1143.0902 16.297 1.43875 94.93 22.60 s12 −33.2088 1.650 1.63775 42.4122.55 s13 89.2116 11.130 1.43875 94.93 23.56 s14 −43.0265 0.110 23.66s15 54.2247 1.430 1.63775 42.41 22.35 s16 22.3467 16.663 1.43875 94.9320.20 s17 −73.4579 0.220 20.17 s18 49.8507 1.100 1.63775 42.41 19.05 s1920.7309 11.427 1.43875 94.93 17.33 s20 −180.4116 1.358 17.18 s21−105.6549 1.100 1.67300 38.15 17.00 s22 111.6317 9.250 16.77 s23−22.2976 0.880 1.48749 70.23 16.77 s24 −115.6031 6.936 1.73800 32.2619.07 s25 −28.8606 0.100 19.39 s26 131.0728 3.590 1.63775 42.41 18.58s27 −126.7311 27.324 18.47 s28 −35.6037 1.100 1.49700 81.54 10.57 s29349.2902 5.126 10.35 s30 −25.0136 1.100 1.49700 81.54 10.07 s31 59.10281.965 1.63775 42.41 10.45 s32 −255.7418 −28.248 10.50

The objective 13 satisfies conditional expressions (1) to (7) and (11)to (16), as described below.

NA=0.95   (1), (4):

FN/|β|/ε =1990   (2):

Φ_(max)/2/h_(exp) /NA=2.95   (3):

f _(G1) /f=3.03   (5):

r ₁₁ /f=−1.45   (6):

r ₁₂ /d ₀₁₂=−1.42   (7):

D _(ogF) /D _(oL)=0.73   (11):

f/f _(G30)=−0.06   (12):

f _(G1) /f _(L2)=0.33   (13):

f _(G1) /f _(L3)=0.25   (14):

f _(G3I) /f=−3.53   (15):

r₂₁ /r ₁₂=1.34   (16):

FIG. 8A to FIG. 8D are aberration diagrams in a case in which acombination of the objective 13 and the tube lens 10 is used. FIG. 8Aillustrates spherical aberration, FIG. 8B illustrates a sine conditionviolation amount, FIG. 8C illustrates astigmatism, and FIG. 8Dillustrates comatic aberration.

EXAMPLE 4

FIG. 9 is a sectional view of an objective 14 in this example. Theobjective 14 illustrated in FIG. 9 is a dry objective for a microscope.The objective 14 is configured of the first lens group G1 with positiverefractive power, the second lens group G2 with positive refractivepower that includes a cemented lens that is configured of a lens withpositive refractive power that is made of a low dispersion material anda lens with negative refractive power that is made of a high dispersionmaterial, and the third lens group G3 with negative refractive power, inorder from the object side.

The first lens group G1 is configured of a meniscus lens L1 (the firstlens) with negative refractive power with a concave surface facing theobject side, a meniscus lens L2 (the second lens) with positiverefractive power with a concave surface facing the object side, ameniscus lens L3 (the third lens component) with positive refractivepower with a concave surface facing the object side, and a meniscus lensL4 (the seventh lens component) with positive refractive power with aconcave surface facing the object side, in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL1that is configured of a biconvex lens L5, a biconcave lens L6, and abiconvex lens L7, and a biconvex lens L8, in order from the object side.The biconvex lens L8 is an aspherical lens for which both surfaces areformed so as to be aspherical.

The third lens group G3 is configured of the 3o-th lens group (the frontlens group), the 3c-th lens group (the intermediate lens group), and the3i-th lens group (the rear lens group), in order from the object side.The 3o-th lens group is configured of a cemented lens CL2 that isconfigured of a meniscus lens L9 (the ninth lens) with negativerefractive power with a concave surface facing the image side and abiconvex lens L10 (the eighth lens), and a cemented lens CL3 that isconfigured of a meniscus lens L11 with negative refractive power with aconcave surface facing the image side and a biconvex lens L12, in orderfrom the object side. The 3c-th lens group is configured of a cementedlens CL4 that is configured of a biconvex lens L13 (the sixth lens;NBH53 of OHARA INC.) and a meniscus lens L14 with negative refractivepower with a concave surface facing the object side, a meniscus lens L15with a concave surface facing the image side, and a meniscus lens L16with a concave surface facing the image side, in order from the objectside. The 3i-th lens group is configured of a biconcave lens L17, and ameniscus lens L18 with positive refractive power with a concave surfacefacing the image side, in order from the object side. The meniscus lensL15, the meniscus lens L16, and the biconcave lens L17 are asphericallenses for which both surfaces are formed so as to be aspherical.

Various pieces of data of the objective 14 are described below. Thed-line (587.56 nm) is used for a reference wavelength.

NA=0.95, FN=30 mm, |β|=20, ε=7.54E−04 mm, f=9 mm, f_(G1)=23.6 mm,r₁₁=−10.2441 mm, r₁₂=−13.3175 mm, d_(o12)=10.314 mm, Φ_(max)/2=21.728mm, h_(exp)=8.55 mm, f_(G30)=909.357 mm, f_(G3I)=−81.92 mm, r₂₁=−17.6973mm, D_(oL)=149.641 mm, D_(ogF)=107.876 mm, f_(L2)=65.24 mm,f_(L3)=175.06 mm

Lens data of the objective 14 is described below. The mark “*” put on asurface number represents that a surface is aspherical.

Objective 14 s r d nd νd er s1(object INF 0.150 1.52100 56.02 0.75surface) s2 INF 2.214 0.87 s3 −10.2441 7.950 1.88300 40.76 4.33 s4−13.3175 0.121 9.56 s5 −17.6973 5.166 1.67790 55.34 10.43 s6 −14.13060.121 12.08 s7 −21.3714 5.186 1.56907 71.30 13.44 s8 −19.1452 0.39615.16 s9 −44.1327 5.129 1.49700 81.54 17.10 s10 −25.6809 0.121 17.75 s1135.9327 14.463 1.49700 81.54 21.12 s12 −54.0221 0.968 1.63775 42.4120.79 s13 30.9878 11.469 1.43875 94.93 20.15 s14 −57.0147 0.121 20.17s15* 762.8936 2.743 1.43875 94.93 19.93 s16* −95.8052 0.121 19.95 s17107.5081 0.968 1.67300 38.15 19.20 s18 20.6405 22.188 1.43875 94.9317.71 s19 −72.7389 0.242 18.35 s20 124.0168 0.968 1.67300 38.15 18.27s21 24.4575 9.958 1.43875 94.93 17.76 s22 −117.0784 0.121 17.84 s232449.3135 16.993 1.73800 32.26 17.93 s24 −24.6714 5.354 1.48749 70.2318.29 s25 −53.1343 2.770 16.63 s26* 683.9611 8.787 1.49700 81.54 14.40s27* 31.7810 2.371 12.29 s28* 22.1813 8.754 1.49700 81.54 11.98 s29*13.6459 5.257 9.41 s30* −33.9011 6.266 1.49700 81.54 9.76 s31* 135.55891.000 10.28 s32 60.0363 1.206 1.73800 32.26 10.50 s33 115.3925 −29.03110.50

Aspherical data of the objective 14 is described below. Here, anaspherical shape is represented by the expression below. In thisexpression, z represents a coordinate in an optical axis direction of anaspherical surface, Y represents a coordinate in a direction orthogonalto an optical axis of the aspherical surface, K represents a conicalcoefficient, r represents a paraxial radius of curvature of theaspherical surface, and A4, A6, A8, and A10 respectively represent thefourth, sixth, eighth, and tenth aspherical coefficients. E represents apower of 10.

$Z = {\frac{Y^{2}}{r + {r\sqrt{1 - {\left( {K + 1} \right)\left( {Y/r} \right)^{2}}}}} + {A\; 4Y^{4}} + {A\; 6Y^{6}} + {A\; 8Y^{8}} + {A\; 10Y^{10}}}$

Fifteenth Surface s15

-   K=−130.5839 A4=−3.374E−06 A6=−2.550E−09 A8=−4.653E−12 A10=−1.689E−14

Sixteenth Surface s16

-   K=0.9776 A4=−1.333E−06 A6=−2.475E−09 A8=−9.516E−12 A10=−6.753E−15

Twenty-Sixth Surface s26

-   K=−115.0934 A4=9.081E−07 A6=−5.191E−08 A8=−1.147E−10 A10=1.250E−13

Twenty-Seventh Surface s27

-   K=−0.5111 A4=1.769E−05 A6=−2.561E−08 A8=−7.502E−10 A10=1.643E−12

Twenty-Eighth Surface s28

-   K=−2.9135 A4=6.461E−07 A6=−2.152E−08 A8=4.242E−10 A10=2.141E−12

Twenty-Ninth Surface s29

-   K=−1.5929 A4=2.967E−05 A6=4.115E−07 A8=3.764E−09 A10=2.546E−11

Thirtieth Surface s30

-   K=−3.3854 A4=1.580E−05 A6=4.658E−07 A8=1.813E−09 A10=−1.025E−11

Thirty-First Surface s31

-   K=−79.1359 A4=-5.487E−06 A6=4.016E−08 A8=4.241E−10 A10=-1.231E−11

The objective 14 satisfies conditional expressions (1) to (7) and (11)to (16), as described below.

NA=0.95   (1), (4):

FN/|β|/ε =1990   (2):

Φ_(max)/2/h_(exp) /NA=2.68   (3):

f _(G1) /f=2.62   (5):

r ₁₁ /f=−1.14   (6):

r ₁₂ /d ₀₁₂=−1.29   (7):

D _(ogF) /D _(oL)=0.72   (11):

f/f _(G30)=−0.01   (12):

f _(G1) /f _(L2)=0.36   (13):

f _(G1) /f _(L3)=0.13   (14):

f _(G3I) /f=−9.10   (15):

r₂₁ /r ₁₂=1.33   (16):

FIG. 10A and FIG. 10D are aberration diagrams in a case in which acombination of the objective 14 and the tube lens 10 is used. FIG. 10Aillustrates spherical aberration, FIG. 10B illustrates a sine conditionviolation amount, FIG. 10C illustrates astigmatism, and FIG. 10Dillustrates comatic aberration.

EXAMPLE 5

FIG. 11 is a sectional view of an objective 15 in this example. Theobjective 15 illustrated in FIG. 11 is a dry objective for a microscope.The objective 15 is configured of the first lens group G1 with positiverefractive power, the second lens group G2 with positive refractivepower that includes a cemented lens that is configured of a lens withpositive refractive power that is made of a low dispersion material anda lens with negative refractive power that is made of a high dispersionmaterial, and the third lens group G3 with negative refractive power, inorder from the object side.

The first lens group G1 is configured of a meniscus lens L1 (the firstlens) with negative refractive power with a concave surface facing theobject side, a meniscus lens L2 (the second lens) with positiverefractive power with a concave surface facing the object side, ameniscus lens L3 (the third lens component) with positive refractivepower with a concave surface facing the object side, and a meniscus lensL4 (the seventh lens component) with positive refractive power with aconcave surface facing the object side, in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL1that is configured of a biconvex lens L5, a biconcave lens L6, and abiconvex lens L7, and a cemented lens CL2 that is configured of ameniscus lens L8 with negative refractive power with a concave surfacefacing the image side and a biconvex lens L9, in order from the objectside.

The third lens group G3 is configured of the 3o-th lens group (the frontlens group), the 3c-th lens group (the intermediate lens group), and the3i-th lens group (the rear lens group), in order from the object side.The 3o-th lens group is configured of a cemented lens CL3 that isconfigured of a meniscus lens L10 (the ninth lens) with negativerefractive power with a concave surface facing the image side and abiconvex lens L11 (the eighth lens), and a biconcave lens L12, in orderfrom the object side. The 3c-th lens group is configured of a cementedlens CL4 (the tenth lens component) that is configured of a meniscuslens L13 with negative refractive power with a concave surface facingthe object side and a meniscus lens L14 (the sixth lens; NBH53 of OHARAINC.) with positive refractive power with a concave surface facing theobject side, and a biconvex lens L15, in order from the object side. The3i-th lens group is configured of a biconcave lens L16, a meniscus lensL17 with negative refractive power with a concave surface facing theobject side, and a diffractive optical element (DOE) L18, in order fromthe object side. The diffractive optical element L18 is an opticalelement in which at least two layers that are made of optical materialsdifferent from each other are laminated, and is a diffractive opticalelement, as described in Japanese Patent No. 3717555, in which a reliefpattern is formed on a boundary surface and diffraction efficiency isenhanced in a wide wavelength region. However, a diffractive opticalelement used for the objective 15 in this example is not limited to thediffractive optical element above. The diffractive optical element maybe a diffractive optical element as described, for example, in JapaneseLaid-Open Patent Publication No. 2003-215457 or Japanese Laid-OpenPatent Publication No. 11-133305.

The diffractive optical element L18 has been designed with an ultra-highindex method, as described, for example, in Japanese Laid-Open PatentPublication No. 8-286113. A surface shape (a radius of curvature and anaspherical coefficient) of the diffractive optical element L18 is a lenssurface shape in a case in which the diffractive optical element L18 isreplaced with a virtual lens (an ultra-high index lens) having extremelygreat refractive power.

Various pieces of data of the objective 15 is described below. Thed-line (587.56 nm) is used for a reference wavelength.

NA=0.95, FN=30 mm, |β|=20, ε=7.54E−04 mm, f=9 mm, f_(G1)=25.9 mm,r₁₁=−11.7553 mm, r₁₂=−16.9884 mm, d_(o12)=14.223 mm, Φ_(max)/2=21.938mm, h_(exp)=8.55 mm, f_(G30)=−102.2878 mm, f_(G31)=−38.562 mm,r₂₁=−23.2686 mm, D_(oL)=151.183 mm, D_(ogF)=102.274 mm, f_(L2)=139.125mm, f_(L3)=104.96 mm

Lens data of the objective 15 is described below. The mark “*” put on asurface number represents that a surface is aspherical. A surface numbers34 indicates a lens surface shape in a case in which a diffractiveoptical element is replaced with a virtual lens (an ultra-high indexlens) having extremely great refractive power.

Objective 15 s r d nd νd er s1(object INF 0.165 1.52103 56.02 0.75surface) s2 INF 1.760 0.88 s3 −11.7553 12.298 1.88306 40.76 3.84 s4−16.9884 0.088 11.65 s5 −23.2686 4.402 1.5691 71.30 12.60 s6 −19.21750.110 14.17 s7 −22.4059 4.840 1.5691 71.30 14.80 s8 −17.5706 0.110 15.53s9 −58.7666 4.091 1.49702 81.54 18.10 s10 −31.1809 0.110 18.44 s1139.7049 15.367 1.43876 94.93 21.02 s12 −30.5156 1.650 1.63779 42.4120.96 s13 123.7205 9.396 1.43876 94.93 21.75 s14 −40.5802 0.110 21.86s15 53.0777 1.430 1.63779 42.41 20.40 s16 20.1928 15.788 1.43876 94.9318.30 s17 −62.8184 0.220 18.26 s18 91.8568 1.100 1.63779 42.41 17.44 s1920.0113 11.538 1.43876 94.93 16.06 s20 −67.1527 0.508 16.00 s21 −56.63301.100 1.63779 42.41 15.97 s22 322.2650 8.580 16.01 s23 −20.5345 0.8231.48751 70.23 16.04 s24 −74.6275 6.688 1.73806 32.26 18.44 s25 −26.51660.194 18.85 s26 136.8083 3.519 1.67305 38.15 18.47 s27 −149.8267 33.11218.38 s28 −60.0182 1.100 1.49702 81.54 11.00 s29 192.7648 6.268 10.82s30 −27.1426 1.100 1.49702 81.54 10.51 s31 −105.6533 1.116 10.74 s32 INF0.500 1.61006 27.48 10.87 s33 INF 0 1000 −3.45 10.90 s34* 2075000 2.0001.63768 34.21 10.90 s35 INF −32.826 11.00

Aspherical data of the objective 15 is described below.

Thirty-Fourth Surface s34

-   K=0 A4=4.591E−11 A6=3.073E−13 A8=0 A10=0

The objective 15 satisfies conditional expressions (1) to (7) and (11)to (16), as described below.

NA=0.95   (1), (4):

FN/|β|/ε =1990   (2):

Φ_(max)/2/h_(exp) /NA=2.70   (3):

f _(G1) /f=2.88   (5):

r ₁₁ /f=−1.31   (6):

r ₁₂ /d ₀₁₂=−1.19   (7):

D _(ogF) /D _(oL)=0.68   (11):

f/f _(G30)=−0.09   (12):

f _(G1) /f _(L2)=0.19   (13):

f _(G1) /f _(L3)=0.25   (14):

f _(G3I) /f=−4.28   (15):

r₂₁ /r ₁₂=1.37   (16):

FIG. 12A to FIG. 12D are aberration diagrams in a case in which acombination of the objective 15 and the tube lens 10 is used. FIG. 12Aillustrates spherical aberration, FIG. 12B illustrates a sine conditionviolation amount, FIG. 12C illustrates astigmatism, and FIG. 12Dillustrates comatic aberration.

EXAMPLE 6

FIG. 13 is a sectional view of an objective 16 in this example. Theobjective 16 illustrated in FIG. 13 is an immersion type objective for amicroscope. The objective 16 is configured of the first lens group G1with positive refractive power, the second lens group G2 with positiverefractive power that includes a cemented lens that is configured of alens with positive refractive power that is made of a low dispersionmaterial and a lens with negative refractive power that is made of ahigh dispersion material, and the third lens group G3 with negativerefractive power, in order from the object side.

The first lens group G1 is configured of a cemented lens CL1 (the firstcemented lens) that is configured of a plano-convex lens L0 with a planesurface facing the object side and a meniscus lens L1 (the first lens)with negative refractive power with a concave surface facing the objectside, a meniscus lens L2 (the second lens) with positive refractivepower with a concave surface facing the object side, a cemented lens CL2(the third lens component) that is configured of a biconcave lens L3 anda biconvex lens L4, and a cemented lens CL3 (the seventh lens component)that is configured of a biconcave lens L5 and a biconvex lens L6, inorder from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL4that is configured of a meniscus lens L7 with positive refractive powerwith a concave surface facing the image side, a meniscus lens L8 withnegative refractive power with a concave surface facing the image side,and a biconvex lens L9, and a three-lens-cemented lens CL5 that isconfigured of a meniscus lens L10 (the sixth lens; TIH53 of OHARA INC.)with positive refractive power with a concave surface facing the imageside, a meniscus lens L11 with negative refractive power with a concavesurface facing the image side, and a biconvex lens L12, in order fromthe object side.

The third lens group G3 is configured of the 3f-th lens group (the frontlens group), the 3m-th lens group (the intermediate lens group), and the3e-th lens group (the rear lens group), in order from the object side.The 3f-th lens group is configured of a meniscus lens L13 (the ninthlens) with negative refractive power with a concave surface facing theimage side, a biconvex lens L14 (the eighth lens), and a cemented lensCL6 that is configured of a meniscus lens L15 with negative refractivepower with a concave surface facing the image side and a meniscus lensL16 with positive refractive power with a concave surface facing theimage side, in order from the object side. The 3m-th lens group isconfigured of a cemented lens CL7 (the twelfth lens component) that isconfigured of a biconvex lens L17 and a biconcave lens L18, and ameniscus lens L19 with negative refractive power with a concave surfacefacing the object side, in order from the object side. The 3e-th lensgroup is configured of a meniscus lens L20 (the eleventh lens component)with negative refractive power with a concave surface facing the imageside, a meniscus lens L21 (the fifth lens component) with negativerefractive power with a concave surface facing the object side, acemented lens CL8 (the fourth lens component) that is configured of ameniscus lens L22 with negative refractive power with a concave surfacefacing the object side and a meniscus lens L23 with positive refractivepower with a concave surface facing the object side, and a biconvex lensL24, in order from the object side.

Various pieces of data of the objective 16 are described below. Thed-line (587.56 nm) is used for a reference wavelength. A refractiveindex N_(o) of immersion liquid is 1.5148.

NA=1.3, FN=30 mm, |β|=40, ε=5.51E−04 mm, f=4.5 mm, f_(G1)=15.83 mm,r₁₂=−6.834 mm, d_(o12)=7.238 mm, Φ_(max)/2=21.64 mm, h_(exp)=5.85 mm,f_(G30)=67.05 mm, D_(oL)=145.000 mm, D_(ogF)=64.477 mm, f_(L2)=51.90 mm,f_(L3)=165.57 mm, f_(L7)=220.49 mm

Lens data of the objective 16 is described below.

Objective 16 s r d nd νd er s1(object INF 0.170 1.52347 54.41 0.38surface) s2 INF 0.362 1.51486 41.00 0.66 s3 INF 0.652 1.51635 64.14 1.29s4 −3.2441 6.054 1.88306 40.76 1.64 s5 −6.8342 0.144 5.90 s6 −16.143511.171 1.5691 71.30 7.68 s7 −13.0577 0.222 12.07 s8 −45.2412 0.8911.63779 42.41 14.57 s9 164.1406 10.007 1.5691 71.30 16.18 s10 −30.45670.122 17.67 s11 −215.6520 0.800 1.63779 42.41 19.01 s12 149.0681 6.9931.5691 71.30 19.59 s13 −72.7399 0.100 20.19 s14 45.7927 4.715 1.4387694.93 21.64 s15 112.1092 0.837 1.63779 42.41 21.59 s16 33.3718 14.1701.43876 94.93 21.26 s17 −61.1831 2.993 21.41 s18 50.0401 4.073 1.8467623.78 20.46 s19 93.4075 1.331 1.75504 52.32 20.00 s20 23.9768 12.1291.43876 94.93 18.15 s21 −90.2641 0.100 17.99 s22 109.2684 0.800 1.7550452.32 17.31 s23 27.2740 0.100 16.40 s24 25.9302 8.731 1.43876 94.9316.55 s25 −111.0317 0.100 16.40 s26 24.1614 2.386 1.75504 52.32 15.02s27 20.4571 11.959 1.43876 94.93 13.89 s28 170.5645 2.268 11.48 s2922.1833 4.491 1.60303 65.44 9.50 s30 −33.1761 2.120 1.73806 32.26 8.95s31 11.7279 4.969 6.73 s32 −14.2396 0.800 1.49702 81.54 6.45 s33−43.4343 15.497 6.51 s34 123.5400 0.800 1.60303 65.44 6.15 s35 14.10453.245 6.08 s36 −12.7149 0.800 1.75504 52.32 6.15 s37 −41.8941 2.177 6.85s38 −10.7606 0.800 1.43876 94.93 6.95 s39 −15.4480 2.076 1.73806 32.267.77 s40 −12.0682 0.100 8.31 s41 64.1504 2.741 1.88306 40.76 10.19 s42−53.5056 −53.273 10.32

Surfaces having surface numbers s1 and s2 are respectively an objectsurface (a surface on the object side of a cover glass) and a surface onthe image side of the cover glass. Surfaces having surface numbers s3and s42 are respectively a lens surface closest to the object and a lenssurface closest to the image plane in the objective. A space between thesurface having a surface number s2 and the surface having a surfacenumber s3 is filled with immersion liquid.

The objective 16 satisfies conditional expressions (1) to (3) and (8) to(14), as described below.

NA=1.3   (1), (8):

FN/|β|/ε−1361   (2):

Φ_(max)/2/h_(exp) /NA=2.85   (3):

f _(G1) /f=3.52   (9):

r ₁₂ /d _(o12)=−0.95   (10):

D _(OgF) /D _(oL)=0.44   (11):

f/f _(G30)=0.07   (12):

f _(G1) /f _(L2)=0.31   (13):

f_(G1) /f _(L3)=0.10   (14):

FIG. 14A to FIG. 14D are aberration diagrams in a case in which acombination of the objective 16 and the tube lens 10 is used. FIG. 14Aillustrates spherical aberration, FIG. 14B illustrates a sine conditionviolation amount, FIG. 14C illustrates astigmatism, and FIG. 14Dillustrates comatic aberration.

EXAMPLE 7

FIG. 15 is a sectional view of an objective 17 in this example. Theobjective 17 illustrated in FIG. 15 is an immersion type objective for amicroscope. The objective 17 is configured of the first lens group G1with positive refractive power, the second lens group G2 with positiverefractive power that includes a cemented lens that is configured of alens with positive refractive power that is made of a low dispersionmaterial and a lens with negative refractive power that is made of ahigh dispersion material, and the third lens group G3 with negativerefractive power, in order from the object side.

The first lens group G1 is configured of a cemented lens CL1 (the firstcemented lens) that is configured of a plano-convex lens L0 with a planesurface facing the object side and a meniscus lens L1 (the first lens)with negative refractive power with a concave surface facing the objectside, a meniscus lens L2 (the second lens) with positive refractivepower with a concave surface facing the object side, a cemented lens CL2(the third lens component) that is configured of a biconcave lens L3 anda biconvex lens L4, and a cemented lens CL3 (the seventh lens component)that is configured of a biconcave lens L5 and a biconvex lens L6, inorder from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL4that is configured of a meniscus lens L7 with positive refractive powerwith a concave surface facing the image side, a meniscus lens L8 withnegative refractive power with a concave surface facing the image side,and a biconvex lens L9, and a three-lens-cemented lens CL5 that isconfigured of a meniscus lens L10 (the sixth lens; TIH53 of OHARA, INC.)with positive refractive power with a concave surface facing the imageside, a meniscus lens L11 with negative refractive power with a concavesurface facing the image side, and a biconvex lens L12, in order fromthe object side.

The third lens group G3 is configured of the 3f-th lens group (the frontlens group), the 3m-th lens group (the intermediate lens group), and the3e-th lens group (the rear lens group), in order from the object side.The 3f-th lens group is configured of a cemented lens CL6 that isconfigured of a meniscus lens L13 (the ninth lens) with negativerefractive power with a concave surface facing the image side and abiconvex lens L14 (the eighth lens), and a cemented lens CL7 that isconfigured of a meniscus lens L15 with negative refractive power with aconcave surface facing the image side and a meniscus lens L16 withpositive refractive power with a concave surface facing the image side,in order from the object side. The 3m-th lens group is configured of acemented lens CL8 that is configured of a meniscus lens L17 withpositive refractive power with a concave surface facing the image sideand a meniscus lens L18 with negative refractive power with a concavesurface facing the image side, and a cemented lens CL9 that isconfigured of a meniscus lens L19 with negative refractive power with aconcave surface facing the object side and a meniscus lens L20 withpositive refractive power with a concave surface facing the object side,in order from the object side. The 3e-th lens group is configured of abiconcave lens L21 (the eleventh lens component), a meniscus lens L22(the fifth lens component) with negative refractive power with a concavesurface facing the object side, a cemented lens CL10 (the fourth lenscomponent) that is configured of a meniscus lens L23 with negativerefractive power with a concave surface facing the object side and ameniscus lens L24 with positive refractive power with a concave surfacefacing the object side, a plano-convex lens L25 with a plane surfacefacing the object side, and a biconvex lens L26, in order from theobject side.

Various pieces of data of the objective 17 are described below. Thed-line (587.56 nm) is used for a reference wavelength. A refractiveindex N_(o) of immersion liquid is 1.5148.

NA=1.4, FN=30 mm, |β|=40, ε=5.12E−04 mm, f=4.5 mm, f_(G1)=14.27 mm,r₁₂=−7.0457 mm, d_(o12)=7.091 mm, Φ_(max)/2=24.721 mm, h_(exp)=6.30 mm,f_(G30)=75.727 mm, D_(oL)=151.261 mm, D_(ogF)=66.140 mm, f_(L2)=47.8 mm,f_(L3)=146.08 mm

Lens data of the objective 17 is described below.

Objective 17 s r d nd νd er s1(object INF 0.170 1.52347 54.41 0.38surface) s2 INF 0.250 1.51486 41.00 0.74 s3 INF 0.541 1.51635 64.14 1.30s4 −3.2573 6.130 1.88306 40.76 1.58 s5 −7.0457 0.101 6.17 s6 −18.260811.223 1.5691 71.30 8.50 s7 −13.3647 0.100 12.69 s8 −47.9736 0.8111.63779 42.41 16.07 s9 156.9755 9.957 1.5691 71.30 18.18 s10 −30.24450.100 19.18 s11 −199.1341 0.800 1.63779 42.41 21.08 s12 143.4114 6.8791.5691 71.30 21.93 s13 −70.9607 0.100 22.34 s14 47.7991 5.342 1.4387694.93 24.60 s15 115.7137 0.801 1.63779 42.41 24.55 s16 34.7896 16.9631.43876 94.93 24.08 s17 −61.7960 2.077 24.23 s18 57.6791 3.796 1.8467623.78 23.09 s19 108.1782 0.918 1.75504 52.32 22.75 s20 26.3280 14.3931.43876 94.93 20.64 s21 −65.8296 0.100 20.57 s22 74.3029 0.810 1.7550452.32 19.11 s23 22.9020 10.684 1.43876 94.93 17.47 s24 −185.2953 0.32417.32 s25 23.7108 2.654 1.75504 52.32 16.10 s26 20.7355 12.324 1.4387694.93 14.89 s27 110.2738 2.752 12.51 s28 19.2575 4.184 1.60303 65.4410.18 s29 1332.6436 2.153 1.73806 32.26 9.49 s30 10.2792 4.211 7.11 s31−21.6113 0.800 1.49702 81.54 7.08 s32 −310.2945 1.098 1.73806 32.26 7.07s33 −94.8995 14.625 7.07 s34 −36.3192 0.800 1.60303 65.44 6.24 s3520.0000 2.657 6.31 s36 −14.2645 0.800 1.75504 52.32 6.35 s37 −44.87292.263 6.99 s38 −10.8850 0.800 1.43876 94.93 7.09 s39 −16.2941 2.0061.73806 32.26 7.94 s40 −12.8173 0.100 8.48 s41 INF 1.594 1.88306 40.769.98 s42 −66.6667 0.100 10.16 s43 84.2007 1.975 1.88306 40.76 10.61 s44−119.1973 −50.823 10.69

The objective 17 satisfies conditional expressions (1) to (3) and (8) to(14), as described below.

NA=1.4   (1), (8):

FN/|β|/ε−1466   (2):

Φ_(max)/2/h_(exp) /NA=2.80   (3):

f _(G1) /f=3.17   (9):

r ₁₂ /d _(o12)=−0.99   (10):

D _(OgF) /D _(oL)=0.44   (11):

f/f _(G30)=0.06   (12):

f _(G1) /f _(L2)=0.30   (13):

f_(G1) /f _(L3)=0.10   (14):

FIG. 16A to FIG. 16D are aberration diagrams in a case in which acombination of the objective 17 and the tube lens 10 is used. FIG. 16Aillustrates spherical aberration, FIG. 16B illustrates a sine conditionviolation amount, FIG. 16C illustrates astigmatism, and FIG. 16Dillustrates comatic aberration.

EXAMPLE 8

FIG. 17 is a sectional view of an objective 18 in this example. Theobjective 18 illustrated in FIG. 17 is an immersion type objective for amicroscope. The objective 18 is configured of the first lens group G1with positive refractive power, the second lens group G2 with positiverefractive power that includes a cemented lens that is configured of alens with positive refractive power that is made of a low dispersionmaterial and a lens with negative refractive power that is made of ahigh dispersion material, and the third lens group G3 with negativerefractive power, in order from the object side.

The first lens group G1 is configured of a cemented lens CL1 (the firstcemented lens) that is configured of a plano-convex lens L0 with a planesurface facing the object side and a meniscus lens L1 (the first lens)with negative refractive power with a concave surface facing the objectside, a meniscus lens L2 (the second lens) with positive refractivepower with a concave surface facing the object side, and a meniscus lensL3 (the third lens component) with positive refractive power with aconcave surface facing the object side, in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL2that is configured of a biconvex lens L4, a biconcave lens L5, and abiconvex lens L6, and a three-lens-cemented lens CL3 that is configuredof a meniscus lens L7 (the sixth lens; TIH53 of OHARA INC.) withpositive refractive power with a concave surface facing the image side,a meniscus lens L8 with negative refractive power with a concave surfacefacing the image side, and a biconvex lens L9, in order from the objectside.

The third lens group G3 is configured of the 3f-th lens group (the frontlens group), the 3m-th lens group (the intermediate lens group), and the3e-th lens group (the rear lens group), in order from the object side.The 3f-th lens group is configured of a cemented lens CL4 that isconfigured of a meniscus lens L10 (the ninth lens) with negativerefractive power with a concave surface facing the image side and ameniscus lens L11 (the eighth lens) with positive refractive power witha concave surface facing the image side, and a cemented lens CL5 that isconfigured of a meniscus lens L12 with negative refractive power with aconcave surface facing the image side and a meniscus lens L13 withpositive refractive power with a concave surface facing the image side,in order from the object side. The 3m-th lens group is configured of acemented lens CL6 (the twelfth lens component) that is configured of ameniscus lens L14 with positive refractive power with a concave surfacefacing the image side and a meniscus lens L15 with negative refractivepower with a concave surface facing the image side, and a cemented lensCL7 that is configured of a meniscus lens L16 with negative refractivepower with a concave surface facing the object side and a meniscus lensL17 with positive refractive power with a concave surface facing theobject side, in order from the object side. The 3e-th lens group isconfigured of a biconcave lens L18 (the eleventh lens component), ameniscus lens L19 (the fifth lens component) with negative refractivepower with a concave surface facing the object side, a meniscus lens L20(the fourth lens component) with negative refractive power with aconcave surface facing the object side, and a meniscus lens L21 withpositive refractive power with a concave surface facing the object side,in order from the object side.

Various pieces of data of the objective 18 are described below. Thed-line (587.56 nm) is used for a reference wavelength. A refractiveindex N_(o) of immersion liquid is 1.5148.

NA=1.3, FN=30 mm, |β|=20, ε=5.51E−04 mm, f=9 mm, f_(G1)=25.5 mm,r₁₂=−15.884 mm, d_(o12)=15.892 mm, Φ_(max)/2=37.6 mm, h_(exp)=11.70 mm,f_(G30)=117 mm, D_(oL)=240.000 mm, D_(ogF)=95.874 mm, f _(L2)=105.04 mm,f_(L3)=121.71 mm

Lens data of the objective 18 is described below.

Objective 18 s r d nd νd er s1(object INF 0.170 1.52347 54.41 0.75surface) s2 INF 0.471 1.51486 41.00 1.03 s3 INF 1.365 1.51635 64.14 1.82s4 −7.1989 13.886 1.88306 40.76 3.00 s5 −15.8839 0.376 12.95 s6 −43.609924.634 1.5691 71.30 17.08 s7 −30.3807 0.142 26.86 s8 −280.6407 10.2291.5691 71.30 33.43 s9 −56.2880 0.195 33.75 s10 122.3257 18.520 1.4387694.93 35.67 s11 −58.5812 1.528 1.63779 42.41 35.65 s12 96.9456 20.0131.43876 94.93 37.30 s13 −68.2221 0.100 37.50 s14 92.5363 4.245 1.8467623.78 36.98 s15 161.2978 0.802 1.75504 52.32 36.81 s16 48.4035 18.5701.43876 94.93 34.52 s17 −179.2671 0.100 34.48 s18 91.9859 0.800 1.7550452.32 32.93 s19 43.7277 13.061 1.43876 94.93 30.99 s20 787.6851 0.10030.90 s21 38.5369 4.195 1.63779 42.41 29.04 s22 29.3182 21.077 1.4387694.93 25.91 s23 187.4254 0.717 23.46 s24 38.5544 9.316 1.49702 81.5420.94 s25 68.6319 5.690 1.73806 32.26 18.05 s26 18.1926 9.271 13.54 s27−30.8961 0.800 1.49702 81.54 13.53 s28 −129.8157 6.381 1.73806 32.2613.80 s29 −48.9189 32.834 14.23 s30 −38.7296 0.800 1.61803 63.33 11.78s31 109.7621 4.288 12.03 s32 −22.5743 0.800 1.75504 52.32 12.06 s33−81.3258 4.884 13.25 s34 −19.1249 4.983 1.73806 32.26 13.48 s35 −20.54770.100 15.77 s36 −7763.5563 4.558 1.88306 40.76 19.18 s37 −52.0532−94.014 19.38

The objective 18 satisfies conditional expressions (1) to (3) and (8) to(14), as described below.

NA=1.3   (1), (8):

FN/|β|/ε−2723   (2):

Φ_(max)/2/h_(exp) /NA=2.47   (3):

f _(G1) /f=2.83   (9):

r ₁₂ /d _(o12)=−1.00   (10):

D _(OgF) /D _(oL)=0.40   (11):

f/f _(G30)=0.08   (12):

f _(G1) /f _(L2)=0.24   (13):

f_(G1) /f _(L3)=0.21   (14):

FIG. 18A to FIG. 18D are aberration diagrams in a case in which acombination of the objective 18 and the tube lens 10 is used. FIG. 18Aillustrates spherical aberration, FIG. 18B illustrates a sine conditionviolation amount, FIG. 18C illustrates astigmatism, and FIG. 18Dillustrates comatic aberration.

EXAMPLE 9

FIG. 19 is a sectional view of an objective 19 in this example. Theobjective 19 illustrated in FIG. 19 is an immersion type objective for amicroscope. The objective 19 is configured of the first lens group G1with positive refractive power, the second lens group G2 with positiverefractive power that includes a cemented lens that is configured of alens with positive refractive power that is made of a low dispersionmaterial and a lens with negative refractive power that is made of ahigh dispersion material, and the third lens group G3 with negativerefractive power, in order from the object side.

The first lens group G1 is configured of a cemented lens CL1 (the firstcemented lens) that is configured of a plano-convex lens L0 with a planesurface facing the object side and a meniscus lens L1 (the first lens)with negative refractive power with a concave surface facing the objectside, a meniscus lens L2 (the second lens) with positive refractivepower with a concave surface facing the object side, a meniscus lens L3(the third lens component) with positive refractive power with a concavesurface facing the object side, and a biconvex lens L4 (the seventh lenscomponent), in order from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL2that is configured of a biconvex lens L5, a biconcave lens L6, and abiconvex lens L7, and a three-lens-cemented lens CL3 that is configuredof a meniscus lens L8 (the sixth lens; TIH53 of OHARA, INC.) withpositive refractive power with a concave surface facing the image side,a meniscus lens L9 with negative refractive power with a concave surfacefacing the image side, and a biconvex lens L10, in order from the objectside.

The third lens group G3 is configured of the 3f-th lens group (the frontlens group), the 3m-th lens group (the intermediate lens group), and the3e-th lens group (the rear lens group), in order from the object side.The 3f-th lens group is configured of a cemented lens CL4 that isconfigured of a meniscus lens L11 (the ninth lens) with negativerefractive power with a concave surface facing the image side and ameniscus lens L12 (the eighth lens) with positive refractive power witha concave surface facing the image side, and a cemented lens CL5 that isconfigured of a meniscus lens L13 with negative refractive power with aconcave surface facing the image side and a meniscus lens L14 withpositive refractive power with a concave surface facing the image side,in order from the object side. The 3m-th lens group is configured of acemented lens CL6 (the twelfth lens component) that is configured of ameniscus lens L15 with positive refractive power with a concave surfacefacing the image side and a meniscus lens L16 with negative refractivepower with a concave surface facing the image side, and a cemented lensCL7 that is configured of a meniscus lens L17 with negative refractivepower with a concave surface facing the object side and a meniscus lensL18 with positive refractive power with a concave surface facing theobject side, in order from the object side. The 3e-th lens group isconfigured of a biconcave lens L19 (the eleventh lens component), ameniscus lens L20 (the fifth lens component) with negative refractivepower with a concave surface facing the object side, a cemented lens CL8(the fourth lens component) that is configured of a meniscus lens L21with negative refractive power with a concave surface facing the objectside and a meniscus lens L22 with positive refractive power with aconcave surface facing the object side, a meniscus lens L23 withpositive refractive power with a concave surface facing the object side,and a biconvex lens L24, in order from the object side.

Various pieces of data of the objective 19 are described below. Thed-line (587.56 nm) is used for a reference wavelength. A refractiveindex N_(o) of immersion liquid is 1.5148.

NA=1.35, FN=30 mm, |β|=20, ε=5.30E−04 mm, f=9 mm, f_(G1)=26.6 mm,r₁₂=−16.1427 mm, d_(o12)=15.983 mm, Φ_(max)/2=42 mm, h_(exp)=12.15 mm,f_(G30)=128.44 mm, D_(oL)=270.000 mm, D_(ogF)=110.373 mm, f_(L2)=108 mm,f_(L3)=145 mm

Lens data of the objective 19 is described below.

Objective 19 s r d nd νd er s1(object INF 0.170 1.52347 54.41 0.75surface) s2 INF 0.500 1.51486 41.00 1.06 s3 INF 1.549 1.51635 64.14 2.01s4 −6.7369 13.764 1.88306 40.76 3.30 s5 −16.1427 0.696 13.61 s6 −40.403424.581 1.5691 71.30 18.50 s7 −29.8313 0.100 27.90 s8 −230.6251 10.8551.5691 71.30 36.23 s9 −61.8679 0.100 36.81 s10 461.9394 3.119 1.569171.30 39.38 s11 −1334.3709 0.100 39.45 s12 111.3362 20.692 1.43876 94.9340.42 s13 −74.6831 5.662 1.63779 42.41 40.37 s14 88.0169 23.795 1.4387694.93 41.63 s15 −78.5986 0.100 41.80 s16 103.7530 4.590 1.84676 23.7840.51 s17 184.2894 2.300 1.75504 52.32 40.33 s18 49.4844 22.221 1.4387694.93 37.07 s19 −150.7597 0.100 37.02 s20 85.8487 2.000 1.75504 52.3234.72 s21 40.6690 14.643 1.43876 94.93 31.78 s22 334.4963 0.100 31.67s23 37.3445 4.191 1.63779 42.41 29.82 s24 29.7904 20.983 1.43876 94.9326.73 s25 138.8114 0.853 24.22 s26 41.3866 8.957 1.49702 81.54 21.79 s2787.4837 5.226 1.73806 32.26 19.18 s28 19.0760 9.956 14.46 s29 −34.44370.900 1.49702 81.54 14.44 s30 −151.4859 2.117 1.73806 32.26 14.74 s31−55.0586 42.292 14.81 s32 −58.6989 0.800 1.61803 63.33 12.63 s33 81.01444.508 12.80 s34 −26.3219 0.900 1.75504 52.32 12.83 s35 −78.6093 4.39513.85 s36 −20.4267 1.009 1.88306 40.76 13.92 s37 −37.4278 4.143 1.7380632.26 15.89 s38 −24.2264 0.100 16.63 s39 −29.1246 2.638 1.63779 42.4117.21 s40 −24.7643 0.100 17.70 s41 422.1492 4.197 1.88306 40.76 20.86s42 −79.2452 −106.731 21.00

The objective 19 satisfies conditional expressions (1) to (3) and (8) to(14), as described below.

NA=1.35   (1), (8):

FN/|β|/ε−2828   (2):

Φ_(max)/2/h_(exp) /NA=2.56   (3):

f _(G1) /f=2.96   (9):

r ₁₂ /d _(o12)=−1.01   (10):

D _(OgF) /D _(oL)=0.41   (11):

f/f _(G30)=0.07   (12):

f _(G1) /f _(L2)=0.25   (13):

f_(G1) /f _(L3)=0.18   (14):

FIG. 20A to FIG. 20D are aberration diagrams in a case in which acombination of the objective 19 and the tube lens 10 is used. FIG. 20Aillustrates spherical aberration, FIG. 20B illustrates a sine conditionviolation amount, FIG. 20C illustrates astigmatism, and FIG. 20Dillustrates comatic aberration.

EXAMPLE 10

FIG. 21 is a sectional view of an objective 20 in this example. Theobjective 20 illustrated in FIG. 21 is an immersion type objective for amicroscope. The objective 20 is configured of the first lens group G1with positive refractive power, the second lens group G2 with positiverefractive power that includes a cemented lens that is configured of alens with positive refractive power that is made of a low dispersionmaterial and a lens with negative refractive power that is made of ahigh dispersion material, and the third lens group G3 with negativerefractive power, in order from the object side.

The first lens group G1 is configured of a cemented lens CL1 (the firstcemented lens) that is configured of a plano-convex lens L0 with a planesurface facing the object side and a meniscus lens L1 (the first lens)with negative refractive power with a concave surface facing the objectside, a meniscus lens L2 (the second lens) with positive refractivepower with a concave surface facing the object side, a meniscus lens L3(the third lens component) with positive refractive power with a concavesurface facing the object side, and a biconvex lens L4 (the seventh lenscomponent), in order from the object side. The biconvex lens L4 is anaspherical lens for which both surfaces are formed so as to beaspherical.

The second lens group G2 is configured of a three-lens-cemented lens CL2that is configured of a biconvex lens L5, a biconcave lens L6, and abiconvex lens L7, and a plano-convex lens L8 with a plane surface facingthe object side, in order from the object side. The plane-convex lens L8is an aspherical lens in which a lens surface of the image side isformed so as to be aspherical.

The third lens group G3 is configured of the 3f-th lens group (the frontlens group), the 3m-th lens group (the intermediate lens group), and the3e-th lens group (the rear lens group), in order from the object side.The 3f-th lens group is configured of a three-lens-cemented lens CL3that is configured of a meniscus lens L9 (the sixth lens; TIH53 ofOHARA, INC.) with positive refractive power with a concave surfacefacing the image side, a meniscus lens L10 with negative refractivepower with a concave surface facing the image side, and a biconvex lensL11, a cemented lens CL4 that is configured of a meniscus lens L12 (theninth lens) with negative refractive power with a concave surface facingthe image side and a meniscus lens L13 (the eighth lens) with positiverefractive power with a concave surface facing the image side, and acemented lens CL5 that is configured of a meniscus lens L14 withnegative refractive power with a concave surface facing the image sideand a meniscus lens L15 with positive refractive power with a concavesurface facing the image side, in order from the object side. The 3m-thlens group is configured of a cemented lens CL6 (the twelfth lenscomponent) that is configured of a meniscus lens L16 with positiverefractive power with a concave surface facing the image side and ameniscus lens L17 with negative refractive power with a concave surfacefacing the image side, and a cemented lens CL7 that is configured of ameniscus lens L18 with negative refractive power with a concave surfacefacing the object side and a meniscus lens L19 with positive refractivepower with a concave surface facing the object side, in order from theobject side. The 3e-th lens group is configured of a biconcave lens L20(the eleventh lens component), a meniscus lens L21 (the fifth lenscomponent) with negative refractive power with a concave surface facingthe object side, a cemented lens CL8 (the fourth lens component) that isconfigured of a meniscus lens L22 with negative refractive power with aconcave surface facing the object side and a meniscus lens L23 withpositive refractive power with a concave surface facing the object side,a meniscus lens L24 with positive refractive power with a concavesurface facing the object side, and a biconvex lens L25, in order fromthe object side. The biconcave lens L20 is an aspherical lens for whichboth surfaces are formed so as to be aspherical. The meniscus lens L21and the biconvex lens L25 are aspherical lenses in which a lens surfaceon the object side is formed so as to be aspherical.

Various pieces of data of the objective 20 are described below. Thed-line (587.56 nm) is used for a reference wavelength. A refractiveindex N_(o) of immersion liquid is 1.5148.

NA=1.45, FN=30 mm, |β|=20, ε=4.94E−04 mm, f=9 mm, f_(G1)=26.9 mm,r₁₂=−14.9778 mm, d_(o12)=16.116 mm, Φ_(max)/2=51.9 mm, h_(exp)=13.05 mm,f_(G30)=94.24 mm, D_(oL)=300.000 mm, D_(ogF)=134.067 mm, f_(L2)=137.033mm, f_(L3)=270.96 mm

Lens data of the objective 20 is described below.

Objective 20 s r d nd νd er s1(object INF 0.170 1.52347 54.41 0.75surface) s2 INF 0.655 1.51486 41.00 1.25 s3 INF 2.192 1.51635 64.14 3.31s4 −7.9038 13.099 1.88306 40.76 4.88 s5 −14.9779 2.533 14.26 s6 −34.146424.266 1.5691 71.30 22.10 s7 −29.8689 0.127 29.68 s8 −211.5322 9.2491.5691 71.30 42.08 s9 −90.6020 0.100 43.14 s10* 206.0617 8.203 1.569171.30 48.83 s11* −902.4320 0.100 48.96 s12 84.4233 29.394 1.43876 94.9351.76 s13 −131.1968 2.488 1.63779 42.41 51.60 s14 77.5618 22.136 1.4387694.93 49.55 s15 −399.1036 2.027 49.60 s16 INF 12.359 1.43876 94.93 49.60s17* −99.6579 0.100 49.60 s18 112.6466 4.869 1.84676 23.78 45.58 s19185.5705 0.800 1.75504 52.32 45.32 s20 44.4911 32.698 1.43876 94.9339.48 s21 −107.8277 0.100 39.44 s22 83.7721 0.800 1.75504 52.32 35.73s23 38.1549 15.109 1.43876 94.93 32.22 s24 141.2766 0.100 32.08 s2532.5170 2.177 1.63779 42.41 30.58 s26 26.0501 24.782 1.43876 94.93 26.04s27 114.8265 0.100 25.08 s28 37.1811 8.297 1.49702 81.54 22.33 s2951.6704 3.874 1.73806 32.26 19.42 s30 17.8456 12.898 14.73 s31 −35.47800.800 1.49702 81.54 14.41 s32 −150.7254 2.764 1.73806 32.26 14.57 s33−61.1012 32.508 14.66 s34* −497.5063 0.800 1.61803 63.33 12.48 s35*29.8465 6.746 12.29 s36* −20.0794 0.800 1.75504 52.32 12.31 s37 −52.39666.143 13.65 s38 −20.6189 0.800 1.88306 40.76 14.61 s39 −34.5889 3.5151.73806 32.26 16.51 s40 −24.7079 0.762 17.12 s41 −94.2453 3.952 1.6377942.41 20.30 s42 −42.7157 0.179 20.66 s43* 112.0266 4.428 1.88306 40.7623.36 s44 −180.0961 −118.512 23.00

Aspherical data of the objective 20 is described below.

Tenth Surface s10

-   K−−0.7052 A4−1.849E−08 A6−−1.547E−11 A8−−1.063E−14 A10−0

Eleventh Surface s11

-   K=−92.9161 A4=2.085E−08 A6=−3.402E−11 A8=−1.112E−14 A10=0

Seventeenth Surface s17

-   K=−0.4340 A4=2.270E−07 A6=1.494E−11 A8=−4.829E−15 A10=0

Thirty-Fourth Surface s34

-   K=−92.9382 A4=−9.240E−06 A6=1.262E−07 A8=−2.565E−10 A10=0

Thirty-Fifth Surface s35

-   K=−3.2850 A4=−1.357E−05 A6=9.443E−08 A8=−2.053E−10 A10=0

Thirty-Sixth Surface s36

-   K=−0.0104 A4=−1.169E−06 A6=−1.636E−08 A8=−9.606E−11 A10=0

Forth-Third Surface s43

-   K=−18.5319 A4=−1.484E−07 A6=0 A8=0 A10=0

The objective 20 satisfies conditional expressions (1) to (3) and (8) to(14), as described below.

NA=1.45   (1), (8):

FN/|β|/ε−3037   (2):

Φ_(max)/2/h_(exp) /NA=2.74   (3):

f _(G1) /f=2.99   (9):

r ₁₂ /d _(o12)=−0.93   (10):

D _(OgF) /D _(oL)=0.45   (11):

f/f _(G30)=0.10   (12):

f _(G1) /f _(L2)=0.20   (13):

f_(G1) /f _(L3)=0.10   (14):

FIG. 22A to FIG. 22D are aberration diagrams in a case in which acombination of the objective 20 and the tube lens 10 is used. FIG. 22Aillustrates spherical aberration, FIG. 22B illustrates a sine conditionviolation amount, FIG. 22C illustrates astigmatism, and FIG. 22Dillustrates comatic aberration.

EXAMPLE 11

FIG. 23 is a sectional view of an objective 21 in this example. Theobjective 21 illustrated in FIG. 23 is an immersion type objective for amicroscope. The objective 21 is configured of the first lens group G1with positive refractive power, the second lens group G2 with positiverefractive power that includes a cemented lens that is configured of alens with positive refractive power that is made of a low dispersionmaterial and a lens with negative refractive power that is made of ahigh dispersion material, and the third lens group G3 with negativerefractive power, in order from the object side.

The first lens group G1 is configured of a cemented lens CL1 (the firstcemented lens) that is configured of a plano-convex lens L0 with a planesurface facing the object side and a meniscus lens L1 (the first lens)with negative refractive power with a concave surface facing the objectside, a meniscus lens L2 (the second lens) with positive refractivepower with a concave surface facing the object side, a cemented lens CL2(the third lens component) that is configured of a biconcave lens L3 anda biconvex lens L4, and a cemented lens CL3 (the seventh lens component)that is configured of a biconcave lens L5 and a biconvex lens L6, inorder from the object side.

The second lens group G2 is configured of a three-lens-cemented lens CL4that is configured of a meniscus lens L7 with positive refractive powerwith a concave surface facing the image side, a meniscus lens L8 withnegative refractive power with a concave surface facing the image side,and a biconvex lens L9, and a three-lens-cemented lens CL5 that isconfigured of a meniscus lens L10 (the sixth lens; TIH53 of OHARA, INC.)with positive refractive power with a concave surface facing the imageside, a meniscus lens L11 with negative refractive power with a concavesurface facing the image side, and a biconvex lens L12, in order fromthe object side.

The third lens group G3 is configured of the 3f-th lens group (the frontlens group), the 3m-th lens group (the intermediate lens group), and the3e-th lens group (the rear lens group), in order from the object side.The 3f-th lens group is configured of a cemented lens CL6 that isconfigured of a meniscus lens L13 (the ninth lens) with negativerefractive power with a concave surface facing the image side and abiconvex lens L14 (the eighth lens), and a cemented lens CL7 that isconfigured of a meniscus lens L15 with negative refractive power with aconcave surface facing the image side and a meniscus lens L16 withpositive refractive power with a concave surface facing the image side,in order from the object side. The 3m-th lens group is configured of acemented lens CL8 (the twelfth lens component) that is configured of abiconvex lens L17 and a biconcave lens L18, and a meniscus lens L19 withnegative refractive power with a concave surface facing the object side,in order from the object side. The 3e-th lens group is configured of abiconcave lens L20 (the eleventh lens component), a meniscus lens L21(the fifth lens component) with negative refractive power with a concavesurface facing the object side, a cemented lens CL9 (the fourth lenscomponent) that is configured of a meniscus lens L22 with negativerefractive power with a concave surface facing the object side and ameniscus lens L23 with positive refractive power with a concave surfacefacing the object side, a biconvex lens L24, and a diffractive opticalelement (DOE) L25, in order from the object side.

Various pieces of data of the objective 21 are described below. Thed-line (587.56 nm) is used for a reference wavelength. A refractiveindex N. of immersion liquid is 1.5148.

NA=1.3, FN=30 mm, |β|=40, ε=5.51E−04 mm, f=4.5 mm, f_(G1)−14.30 mm,r₁₂−−6.990 mm, d_(o12)−7.199 mm, Φ_(max)/2−21.32 mm, h_(exp)=5.85 mm,f_(G30)=69.74 mm, D_(oL)=145.000 mm, D_(ogF)=65.076 mm, f_(L2)=49.55 mm,f_(L3)=117.33 mm

Lens data of the objective 21 is described below. A surface number s44indicates a lens surface shape in a case in which a diffractive opticalelement is replaced with a virtual lens (an ultra-high index lens)having extremely great refractive power.

Objective 21 s r d nd νd er s1(object INF 0.170 1.52347 54.41 0.38surface) s2 INF 0.333 1.51486 41.00 0.66 s3 INF 0.618 1.51635 64.14 1.24s4 −3.2999 6.078 1.88306 40.76 1.59 s5 −6.9896 0.121 5.91 s6 −17.452811.219 1.5691 71.30 7.74 s7 −13.2943 0.194 12.15 s8 −48.9021 0.9801.63779 42.41 14.73 s9 146.3471 10.058 1.5691 71.30 16.37 s10 −28.26150.100 17.61 s11 −141.0081 0.802 1.63779 42.41 18.79 s12 100.4622 6.3541.5691 71.30 19.57 s13 −70.7737 0.100 19.90 s14 44.9582 5.106 1.4387694.93 21.32 s15 106.1692 2.298 1.63779 42.41 21.26 s16 32.5030 13.6131.43876 94.93 20.84 s17 −63.5018 2.579 20.97 s18 52.2478 4.354 1.8467623.78 20.20 s19 112.2228 1.743 1.75504 52.32 19.73 s20 24.7453 11.4911.43876 94.93 17.94 s21 −82.1758 0.100 17.81 s22 81.6786 0.803 1.7550452.32 16.99 s23 24.9223 8.083 1.43876 94.93 15.97 s24 −136.1825 0.10015.84 s25 23.8425 2.286 1.75504 52.32 14.71 s26 19.9624 12.027 1.4387694.93 13.63 s27 162.1933 2.258 11.34 s28 21.5140 4.479 1.60303 65.449.49 s29 −43.3478 2.154 1.73806 32.26 8.85 s30 11.2466 3.863 6.73 s31−18.7530 0.962 1.49702 81.54 6.66 s32 −43.9945 13.831 6.68 s33 −64.03430.800 1.60303 65.44 5.86 s34 17.2665 3.000 5.86 s35 −10.9759 0.8401.75504 52.32 5.91 s36 −32.8559 1.928 6.66 s37 −10.5993 0.879 1.4387694.93 6.76 s38 −14.9478 2.126 1.73806 32.26 7.56 s39 −11.6319 0.100 8.11s40 89.1554 2.572 1.88306 40.76 9.75 s41 −43.4106 1.000 9.89 s42 INF0.500 1.61006 27.48 10.06 s43 INF 0 1000 −3.45 10.09 s44* 6076000 2.0001.63768 34.21 10.09 s45 INF −51.001 10.19

Aspherical data of the objective 21 is described below.

Forty-Fourth Surface s44

-   K=0 A4=1.645E−10 A6=8.451E−13 A8=0 A10=0

The objective 21 satisfies conditional expressions (1) to (3) and (8) to(14), as described below.

NA=1.3   (1), (8):

FN/|β|/ε−1361   (2):

Φ_(max)/2/h_(exp) /NA=2.80   (3):

f _(G1) /f=3.18   (9):

r ₁₂ /d _(o12)=−0.97   (10):

D _(OgF) /D _(oL)=0.45   (11):

f/f _(G30)=0.06   (12):

f _(G1) /f _(L2)=0.29   (13):

f_(G1) /f _(L3)=0.12   (14):

FIG. 24A to FIG. 24D are aberration diagrams in a case in which acombination of the objective 21 and the tube lens 10 is used. FIG. 24Aillustrates spherical aberration, FIG. 24B illustrates a sine conditionviolation amount, FIG. 24C illustrates astigmatism, and FIG. 24Dillustrates comatic aberration.

Lastly, the tube lens 10 illustrated in FIG. 3, which is used in commonin Example 1 to Example 11, is described. The tube lens 10 is a tubelens for a microscope that is used in combination with an infinitycorrection type objective so as to form a magnified image of an object.The tube lens 10 is configured of the first lens group G1 with positivepower that includes a cemented lens CL1, the second lens group G2 withnegative power, and the third lens group G3 having positive power as awhole that is configured of a plurality of lenses (L6 and L7) that eachhave positive power, in order from the object side.

The first lens group G1 is configured of a biconvex lens L1, and acemented lens CL1 that is configured of a biconvex lens L2 and abiconcave lens L3, in order from the object side. The second lens groupG2 is configured of a cemented lens CL2 that is configured of abiconcave lens L4 and a biconvex lens L5, in order from the object side.The third lens group G3 is configured of a meniscus lens L6 withpositive power with a concave surface facing the object side, and abiconvex lens L7, in order from the object side. Each of the first lensand the second lens has a meniscus shape.

Lens data of the tube lens 10 is described below. “INF” in the lens datarepresents infinity (∞).

Tube lens 10 s r d nd νd s1 INF 162.2 s2 63.8523 9.3326 1.497 81.54 s3−1485.8995 3.1666 s4 39.1423 13.9864 1.497 81.54 s5 −145.3496 6 1.5163364.14 s6 26.8639 20.2953 s7 −53.5928 8.0905 1.72047 34.71 s8 110.31067.877 1.43875 94.93 s9 −130 14.8023 s10 −288.1082 6 1.59522 67.74 s11−114.1428 0.4703 s12 176.2945 6 1.85026 32.27 s13 −475.1754

What is claimed is:
 1. A dry objective for a microscope, the dryobjective comprising in order from an object side: a first lens groupwith positive refractive power; a second lens group with positiverefractive power, the second lens group including a cemented lens thatis configured of a lens with positive refractive power that is made of alow dispersion material and a lens with negative refractive power thatis made of a high dispersion material; and a third lens group withnegative refractive power, wherein: the first lens group includes inorder from the object side: a first lens that is a single lens having ameniscus shape with a concave surface facing the object side; a secondlens that is a single lens with positive refractive power, the singlelens having a meniscus shape with a concave surface facing the objectside; and a third lens component that is a single lens or cemented lenswith positive refractive power, the dry objective is configured in amanner such that a ray height of an on-axis marginal ray becomes maximumon a boundary surface of a lens component closest to an object in thesecond lens group or within the lens component, and when NA represents anumerical aperture of the objective, f represents a focal length of theobjective, f_(G1) represents a focal length of the first lens group, r₁₁represents a radius of curvature of a lens surface on the object side ofthe first lens, r₁₂ represents a radius of curvature of a lens surfaceon an image side of the first lens, and d_(o12) represents a distance onan optical axis from a front-side focal plane of the objective to a lenssurface on the image side of the first lens, the objective satisfies thefollowing conditional expressions:0.8≦NA<1   (4)1.6≦f _(G1) /f≦6   (5)−1.6≦r ₁₁ /f≦−0.2   (6)−2≦r ₁₂ /d _(o12)≦−0.86   (7).
 2. The objective according to claim 1,wherein the third lens component has a meniscus shape with a concavesurface facing the object side.
 3. The objective according to claim 1,wherein the second lens group includes a three-lens-cemented lens thatis formed by respectively cementing lenses with positive refractivepower that are made of a low dispersion material to both surfaces of alens with negative refractive power that is made of a high dispersionmaterial.
 4. The objective according to claim 2, wherein the second lensgroup includes a three-lens-cemented lens that is formed by respectivelycementing lenses with positive refractive power that are made of a lowdispersion material to both surfaces of a lens with negative refractivepower that is made of a high dispersion material.
 5. The objectiveaccording to claim 1, wherein the first lens group includes a seventhlens component that is a single lens or cemented lens with positiverefractive power, closer to the image side than the third lenscomponent.
 6. The objective according to claim 2, wherein the first lensgroup includes a seventh lens component that is a single lens orcemented lens with positive refractive power, closer to the image sidethan the third lens component.
 7. The objective according to claim 3,wherein the first lens group includes a seventh lens component that is asingle lens or cemented lens with positive refractive power, closer tothe image side than the third lens component.
 8. The objective accordingto claim 4, wherein the first lens group includes a seventh lenscomponent that is a single lens or cemented lens with positiverefractive power, closer to the image side than the third lenscomponent.
 9. The objective according to claim 1, wherein: the thirdlens group includes a front lens group closest to the object side, thefront lens group includes: an eighth lens with positive refractive powerthat is made of a low dispersion material; and a ninth lens withnegative refractive power that is made of a high dispersion material,the eighth lens and the ninth lens being arranged so as to be adjacentto each other, a lens surface on a ninth-lens side of the eighth lensand a lens surface on an eighth lens-side of the ninth lens have aradius of curvature having the same sign, and when f_(G30) represents afocal length of the front lens group, the objective satisfies thefollowing conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 10. The objective according to claim 2,wherein: the third lens group includes a front lens group closest to theobject side, the front lens group includes: an eighth lens with positiverefractive power that is made of a low dispersion material; and a ninthlens with negative refractive power that is made of a high dispersionmaterial, the eighth lens and the ninth lens being arranged so as to beadjacent to each other, a lens surface on a ninth-lens side of theeighth lens and a lens surface on an eighth lens-side of the ninth lenshave a radius of curvature having the same sign, and when f_(G30)represents a focal length of the front lens group, the objectivesatisfies the following conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 11. The objective according to claim 3,wherein: the third lens group includes a front lens group closest to theobject side, the front lens group includes: an eighth lens with positiverefractive power that is made of a low dispersion material; and a ninthlens with negative refractive power that is made of a high dispersionmaterial, the eighth lens and the ninth lens being arranged so as to beadjacent to each other, a lens surface on a ninth-lens side of theeighth lens and a lens surface on an eighth lens-side of the ninth lenshave a radius of curvature having the same sign, and when f_(G30)represents a focal length of the front lens group, the objectivesatisfies the following conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 12. The objective according to claim 4,wherein: the third lens group includes a front lens group closest to theobject side, the front lens group includes: an eighth lens with positiverefractive power that is made of a low dispersion material; and a ninthlens with negative refractive power that is made of a high dispersionmaterial, the eighth lens and the ninth lens being arranged so as to beadjacent to each other, a lens surface on a ninth-lens side of theeighth lens and a lens surface on an eighth lens-side of the ninth lenshave a radius of curvature having the same sign, and when f_(G0)represents a focal length of the front lens group, the objectivesatisfies the following conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 13. The objective according to claim 5,wherein: the third lens group includes a front lens group closest to theobject side, the front lens group includes: an eighth lens with positiverefractive power that is made of a low dispersion material; and a ninthlens with negative refractive power that is made of a high dispersionmaterial, the eighth lens and the ninth lens being arranged so as to beadjacent to each other, a lens surface on a ninth-lens side of theeighth lens and a lens surface on an eighth lens-side of the ninth lenshave a radius of curvature having the same sign, and when f_(G30)represents a focal length of the front lens group, the objectivesatisfies the following conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 14. The objective according to claim 6,wherein: the third lens group includes a front lens group closest to theobject side, the front lens group includes: an eighth lens with positiverefractive power that is made of a low dispersion material; and a ninthlens with negative refractive power that is made of a high dispersionmaterial, the eighth lens and the ninth lens being arranged so as to beadjacent to each other, a lens surface on a ninth-lens side of theeighth lens and a lens surface on an eighth lens-side of the ninth lenshave a radius of curvature having the same sign, and when f_(G30)represents a focal length of the front lens group, the objectivesatisfies the following conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 15. The objective according to claim 7,wherein: the third lens group includes a front lens group closest to theobject side, the front lens group includes: an eighth lens with positiverefractive power that is made of a low dispersion material; and a ninthlens with negative refractive power that is made of a high dispersionmaterial, the eighth lens and the ninth lens being arranged so as to beadjacent to each other, a lens surface on a ninth-lens side of theeighth lens and a lens surface on an eighth lens-side of the ninth lenshave a radius of curvature having the same sign, and when f_(G30)represents a focal length of the front lens group, the objectivesatisfies the following conditional expression:−0.3≦f/f _(G30)≦0.3   (12).
 16. The objective according to claim 1,wherein: the third lens group includes a rear lens group with negativerefractive power closest to the image side, and when f_(G3I) representsa focal length of the rear lens group, the objective satisfies thefollowing conditional expression:−10≦f _(G3I) /f≦−1.5   (15).
 17. The objective according to claim 16,wherein the rear lens group includes two or more lens components withnegative refractive power.
 18. The objective according to claim 16,wherein: the third lens group includes: a front lens group arrangedclosest to the object side; and an intermediate lens group arrangedbetween the front lens group and the rear lens group, and theintermediate lens group includes a tenth lens component that isconfigured of a single lens or cemented lens having a meniscus shapewith a concave surface facing the object side.
 19. The objectiveaccording to claim 1, wherein when r₁₂ represents the radius ofcurvature of the lens surface on the image side of the first lens, andr₂₁ represents a radius of curvature of a lens surface on the objectside of the second lens, the objective satisfies the followingconditional expression:0.8≦r ₂₁ /r ₁₂≦2   (16).
 20. The objective according to claim 1, whereina lens component closest to an image plane in the second lens group is alens component with positive refractive power that is closest to theobject among lens components other than lens components included in thefirst lens group and a lens component which the maximum ray height ofthe on-axis marginal ray passes through.